The movie begins by showing a young woman, Na Ji Young, about to sleep in her room after reading
a message from her ex-boyfriend, who wants to get back to her. Ji Young was a very individualistic
introverted woman and often avoided social interaction with other people. Since graduating
from college, she has lived alone in an apartment and worked in a hospital as a nurse. That night,
her neighbor, Byeok Su, came to Ji Young room to ask for the wifi password. In contrast to her,
Byeok Su was an extroverted young man with a warm personality and was good at getting along with
others. He had a girlfriend named Ye Jin who lived with him, but their relationship has been strained
and not harmonious lately. Feeling annoyed with Byeok Su, Ji Young immediately turned off the
phone and returned to bed to continue her delayed sleep. She tried to go to bed early but still had
trouble sleeping due to severe insomnia she had suffered since she was a teenager. Ji Young often
visited a psychiatrist to overcome her insomnia for consultation and hypnotherapy. Over the past
few weeks, she had been seeing a psychiatrist, Jung So Kyung, regularly to consult her problems.
Psychiatrist Jung ordered Ji Young to always be active and keep a daily journal to find the source
of the problem or trauma that was bothering her mind. Every day, as a neighbor who lived in the
same apartment, Byeok Su tried to be friendly and greet Ji Young. But she always ignored him
and never even responded to his greeting. One day, Byeok Su asked a courier to leave a package with
her, but she didn't care about it and left the package at the door. That night, when Byeok Su was
about to take the package, Ji Young said that she had placed the package in front of his door. As a
result, when Byeok Su told his girlfriend that the package had disappeared, Ye Jin was immediately
furious with Byeok Su. In the end, Ye Jin, fed up with the conflict between Ji Young and Byeok Su,
decides to end the relationship and leave Byeok Su. Ji Young got into a problem different
from Byeok Su's. Her ex-boyfriend, Yeon Suk, kept persuading her to get back into a relationship,
but she refused. Both Byeok Su and Yeon Suk kept begging their respective girlfriends to get back,
causing a commotion in the apartment. Starting to feel uncomfortable with their boyfriend's
behavior, Ji Young and Ye Jin took them to the police station. The police ended up
detaining Byeok Su for one day, while Yeon Suk got a warning to never harass Ji Young again.
The following day, Ji Young called the apartment locksmith to reset her key password so Yeon Suk
could not barge in. Not long after, Byeok Su, who was out of prison, came to Ji Young with
feelings of annoyance because he thought she was the cause of his breakup with his girlfriend. But
Ji Young again didn't care and chose to leave him. At night, Byoek Su, who felt heartbroken and lost,
drank a lot to forget his problem. He even entertained himself by watching a movie in
the cinema, but it didn't work because it made him remember everything. Byeok Su felt lonely
and unable to live alone. He tried to forgive Ji Young and get closer to her. Unfortunately,
he found it difficult to approach her. Ji Young was very individualistic and didn't want to mingle
with others. But one night, when Byeok Su was watching a movie at the cinema, he accidentally
met Ji Young in the same row of seats. Feeling afraid of the horrific scene, Byeok Su slowly
began to approach Ji Young and subconsciously sat beside her. Ji Young felt uncomfortable and tried
to avoid him. But she finally gave up because he kept coming to her. She was increasingly irritated
by Byeok Su, who secretly drank her soda. On the way back to the apartment, Byeok Su followed Ji
Young again and tried to talk to her. However, she kept avoiding and ignoring him. Byeok Su was
confused by Ji Young, who was always cold to him. Upon arriving at the apartment elevator, Byeok Su
realized that he had drunk soda from the same straw as Ji Young and immediately assumed they had
kissed indirectly. He thought that the kiss was what made her annoyed with him. Ji Young denied
it and said that she would only think of the kiss as kissing an animal. Those words clearly
made Byeok Su even more annoyed with her. They then started arguing again before entering their
rooms. They were still arguing and banging on the walls to vent their anger. The following day,
Ji Young saw psychiatrist Jung again to submit the daily journal she had been writing for the past
week. After reading the diary, psychiatrist Jung realized that Ji Young was still hiding something
about her past and trauma. She then asks Ji Young to learn to be honest with herself because a
psychiatrist could not help if their patients were still hiding something about their problems. That
afternoon when Ji Young came home from the hospital, her stomach suddenly felt queasy,
so she dashed to her apartment. However, in front of the apartment, Yeon Suk again
begged her to continue their relationship. While holding her stomach, Ji Young tried to avoid him,
but he kept following her. Ji Young then accidentally fell and farted before him. She felt
embarrassed and immediately ran into the apartment and rushed to her room. Unfortunately, Ji Young
suddenly forgot her door password, forcing her to enter Byeok Su's apartment. She, by chance,
had seen his door password. Byeok Su, who was in the apartment, heard the sound of an intruder
entering his bathroom. He immediately took a racket and broke down the bathroom door to catch
the intruder. He accidentally saw Ji Young in his bathroom. Seeing Byeok Su, Ji Young screamed and
closed the bathroom door. Byeok Su, who initially panicked, started laughing when he discovered that
Ji Young had a minor accident in her pants. He started mocking her while laughing with
satisfaction. Ji Young could only remain silent while holding back the great embarrassment. Byeok
Su then called the apartment locksmith to open Ji Young's door to get clean pants for her. Before he
entered the room, Ji Young had warned him not to open her things. However, after he took the pants,
he opened Ji Young's cell phone even though he had been warned not to do that. After the embarrassing
incident, Ji Young could only curse herself for feeling so ashamed. Byeok Su just smiled,
amused every time he remembered it. The following day, Byeok Su visited his parent. His mother had
prepared a stock of kimchi and other food for him, while his younger sister asked for some
pocket money. There, his mother invited him to go on holiday on Christmas Day. He happily accepted
the invitation. One day, Ji Young went to the tenant's office and planned to move to another
apartment because her neighbor was too noisy. However, the manager said that Byeok Su was also
planning to move because he could not afford to pay the rent. Knowing this, Ji Young canceled her
intention to move, considering that her goal of moving was to get away from Byeok Su. That
afternoon when Ji Young was about to go to the supermarket, Byeok Su accidentally saw her. He
then followed her shopping at the supermarket. He tried hard to be friendly to Ji Young and
invited her to spend time together on Christmas. Byeok Su seemed to have forgotten that he had an
appointment with his family on Christmas Day. Then, Ji Young realized that Byeok Su had been
peeking at her things without permission. She was angry and immediately scolded him. She even said
hurtful words and offered some money to him while asking him not to come near her again. Seeing her
outrageous attitude, Byeok Su felt hurt and chose to leave her. Unfortunately, not long after that,
Byeok Su got news from his mother that they had canceled their vacation invitation because his
sister didn't want him to come with them. While holding back tears, Byeok Su could remain silent
and not say anything. He realized that he was just an adopted son, so it was natural that they
behaved that way. When Christmas Day arrived, Byeok Su spent his time in his room. He watched
movies on his laptop while eating some snacks. He looked at his cell phone sometime and checked
messages, and no one called or asked him to go out. It was later revealed that although Byeok
Su has a friendly personality, not many people like him, and they actually take advantage of
him more. On the other hand, Ji Young had also gotten used to spending Christmas Eve alone in her
room for the past few years. That night, Ji Young felt a little surprised because there was a sound
behind the wall of Byeok Su's room. She thought that on that day, Byeok Su would go on vacation
with his family. She then turned on her favorite music, put on earplugs, and took sleeping pills to
sleep well. Since she forgot that the dose of her sleeping pills had increased, she took two pills
instead, so she started having hallucinations. She saw a kitten on her stomach, and she tried to
pet the kitten, but her hands went limp and fell on the stereo remote. She accidentally turned up
the music volume. Byeok Su, who was in the next room, started to get distracted because the music
was too loud. He knocked on Ji Young's door and asked her to turn down her music. Since there was
no response, Byeok Su worried that something had happened to Ji Young. He was panicking and tried
to enter the room using the initial password. Fortunately, Ji Young had not changed the password
so he could open the door. Meanwhile, Ji Young, still unconscious, had a strange dream where she
returned to the past when she was seven years old. It was Christmas day, when every child should feel
happy gathering with their families. But little Ji Young couldn't feel that happiness because
her parents were too busy fighting. Little Ji Young then approached her mother and asked about
the kitten she had asked for from Santa Claus. But her mother scolded her and said that Santa
wasn't real. Since then, Ji Young has never liked Christmas Eve and has grown into a girl who is
very closed off from others. Even one night, when she saw her father having an affair with another
woman, she didn't seem to care about it and ignored him. Every time she came home from school,
Ji Young had to witness her parent's fight. They were getting increasingly disharmonious. One day,
her father and mother argued about who would care for her because they didn't want to take
responsibility. Since then, Ji Young has decided to live alone without her parents. The only thing
that made her happy was the stray cat she found on the street. Since Ji Young left her parents,
she had always thought that asking for mercy only showed her weakness in front of other people.
Therefore, she always acted cold and pretended to be tough to avoid being pitied by others. When Ji
Young woke up from fainting, she saw Byeok Su in her room and panicked while calling an ambulance.
She asked him what he was doing in her room. Byoek Su immediately hung up his phone while
breathing a sigh of relief, knowing that Ji Young was fine. Worried about Ji Young's condition,
Byeok Su scolded her for not changing the door password and didn't link her apartment's key
chain. Seeing the attention shown by Byeok Su, Ji Young apologized for hating him for no apparent
reason. It was then that Byeok Su realized that even though Ji Young often acted cold and aloof,
she actually had a soft heart and was understanding to others. Byeok Su then
opened up about his family and his adoption status to Ji Young and told her that he also
often felt alone like her. Hearing his story, Ji Young realizes that they both have almost the same
fate where their parents abandoned them. After that, Ji Young awkwardly asked Byeok Su to sleep
beside her and spend Christmas Eve together. At first, Byeok Su still didn't understand, so he
intended to return to his room. But then he was shocked after realizing what she meant. He again
asked Ji Young if she really wanted to sleep with him. After spending the night together, Ji Young
immediately threw Byeok Su away. He could only smile in amusement at her ridiculous behavior.
The following day when Ji Young was about to go to work, she accidentally met Byeok Su in front of
the elevator. She saw the couple's ring that Byeok Su was wearing. Ji Young, who started liking him,
became annoyed and jealous at Byeok Su's still wearing his ex-girlfriend's ring. She then told
him that what happened last night was just a momentary relationship, and she asked him not
to get too close to her. Feeling confused by Ji Young's wishy-washy attitude, Byeok Su shared this
with his co-workers at the office. His friends instantly realized that the cause of Ji Young's
irritation was that his ex's ring was still on his finger. Byeok Su felt relieved and smiled happily
after knowing that Ji Young was acting this way because she was jealous. On the other hand,
Ji Young continued to be haunted by the image of Byeok Su showing off his couple's ring. While
working at the hospital, she kept imagining Byeok Su's presence mocking her, which really disturbed
her mind. At night after the work shift ended, Ji Young followed Byeok Su's advice to get along with
the other nurse colleagues. Since then, she got close to a nurse named Park and learned to mingle
with the people around her. In the evening, when Ji Young was going to return to the apartment,
she was again made jealous by Byeok Su's closeness to his female friend. It turned out that Byeok Su
deliberately asked the woman for help to pretend to be his close friend to find out Ji Young's true
heart. A few days later, Byeok Su moved out of his apartment, pretended to be indifferent to her,
and left without saying goodbye. Byeok Su's sudden departure made Ji Young feel very sad and
lost because he had made her life more colorful over the past few days. At that moment, Byeok
Su came to Ji Young's apartment and pretended he didn't have a place to live. He reasoned that his
apartment was still being renovated. Ji Young was excited him. But she hid her feeling and pretended
to be indifferent in front of Byeok Su. Initially, Ji Young refused to accommodate Byeok Su,
but seeing his pitiful face, she changed her mind and allowed him to stay there for some time. She
said she worked the night shift so he could use her nighttime apartment to rest. Byeok Su happily
accepted the offer so he could always meet Ji Young. As time passed, the relationship between
Ji Young and Byeok Su became closer. They began to accept each other. Ji Young was relieved that
living with other people was not as bad as she had imagined. She even started to be friendly
to Byeok Su and occasionally invited him to go out for dinner. One day when they were shopping,
Byeok Su got into trouble by wearing his ex's ring. Ji Young, who felt annoyed, immediately
took the ring and threw it on the floor before she finally left Byeok Su. Instead of being angry with
her attitude, Byeok Su was happy and increasingly convinced that she liked him. That night,
Byeok Su immediately chased Ji Young and dared to confess his feelings to her. But strangely,
she rejected him because she was still unsure if he loved her. Byeok Su reassured her by showing
his sincerity. But Ji Young was still afraid that her attitude would hurt him in the future. Byeok
Su didn't care about that and said that she didn't need to change because he would try to understand
her. Hearing Byeok Su's sincerity, Ji Young decided to give him a chance and accept him as her
boyfriend. Since that day, Byeok Su and Ji Young started living their daily lives as a couple and
learned to understand each other. Ji Young began to forget the wounds and trauma she experienced
and thought she could find new happiness with Byeok Su. One day, Byeok Su accidentally found
Ji Young's diary and decided to read it without her knowledge. It was then that he found out that
Ji Young had to grow alone all this time and was deeply saddened by the wounds she experienced in
the past. Byeok Su then met Jung's psychiatrist. He wanted to know about Ji Young's condition and
consulted on how to help her recover from the trauma. After returning from the consultation,
Byeok Su told Ji Young that he would always be by her side and protect her forever. He was hoping
she could open up about the old wounds and be willing to share any troubles she went through.
The following day, Ji Young's mother suddenly came to see her, and apparently, Ji Young was
still unable to forgive her. Her mother could say anything. Ji Young angrily said she had already
paid for all the living expenses her mother gave her in the past. She thought that was enough to
end their relationship. Over the years, her mother often asked Ji Young for money, and she was forced
to give it, hoping she could release her bond with her mother. But that day, her mother did not
come to ask for money but told Ji Young that her father was sick. Byeok Su, who knew about this,
mediated their quarrel and persuaded Ji Young to visit her parents. Unfortunately,
Ji Young didn't take the suggestion well because she still couldn't reinstate her parents,
who had abandoned her for years. Byeok Su didn't give up and kept persuading Ji Young to forgive
her parents and started learning to forget her past. It was not an easy thing for Ji Young. She
was angry with Byeok Su and kicked him out of her apartment. Byeok Su then left Ji Young, feeling
disappointed because she still hadn't opened up to him and didn't want to let him help. Since
Byeok Su left, Ji Young deleted all the memorable pictures from her cellphone and even deleted Byeok
Su's contact. She returned to being the old Ji Young, where she was always cold and indifferent
to the people around her. She continued to live that way until one day, a patient she treated at
the hospital awakened her. The young girl she was taking care of said she didn't deserve to
live because no one cared for her. These words then made Ji Young feel very sad. She was afraid
that the same thing would happen to her. Ji Young immediately turned around and burst into tears,
lamenting that she had kicked Byeok Su out, the only person who truly cared about her. She then
ran to the locker room and called Byeok Su. She couldn't remember Byeok Su's phone number,
so she just cried. Nurse Park, who knew Ji Young was crying in the locker room, approached and
calmed her down with a warm hug. The following day, Ji Young went to see Psychiatrist Jung
and told her about all the past wounds she had been hiding alone. She shared that her parents
had never been there for her all this time, and she only pretended to be tough in front of other
people to cover up her sadness. She also revealed that she could feel happiness for the first time
with Byeok Su. He was an important person who made her life more beautiful. A few days later,
Ji Young visited her father's grave. He died some time ago. Ji Young learned to be open with the
world around her and tried to forgive her mother, even though it all took a long time. Ji Young gave
psychiatrist Jung a gift for all the help that she had given her. Psychiatrist Jung then said
that Ji Young should give the gift to someone who had just come to her office and asked how she
was. Hearing this, Ji Young immediately realized that the person was Byeok Su. She instantly ran
outside the building to find him. When Ji Young saw Byeok Su board the train from a distance,
she rushed to the train. But she fell to the floor and started to lose hope of being able to meet him
again. Not long after, she heard someone calling her, and when she turned around, it was Byeok Su.
The film ends with a happy ending where Ji Young and Byeok Su reunite and live happily. The moral
that can be learned from this movie is that being alone and avoiding people might protect
us from hurt and pain. However, being alone will also keep us away from affection and love.