One of Jakob's ten heuristics for UI design is to maintain consistency and adhere to standards.
This heuristic is crucial for ensuring that your UI is predictable and learnable.
People shouldn't have to wonder whether different words, symbols, situations, or actions
mean the same thing.
We can think about two types of consistency as it applies to UX design:
internal consistency and external consistency.
Internal consistency refers to maintaining consistency within a product or family of products.
For example, maybe your visual designers decide to use a specific shade of orange to
highlight actionable elements: things like call-to-action buttons.
If you decided to then use that orange to highlight a static heading, you'd be breaking internal consistency.
That might be a problem because it violates the established meaning of that visual treatment.
Users may no longer be able to rely on it to help them determine which elements in your UI are actionable.
External consistency refers to maintaining consistency outside of products.
You might have established conventions for UIs in your industry,
or even established conventions for UIs in general.
For example most ecommerce sites have a shopping cart feature.
People are familiar with this feature because they see it anytime they use an e-commerce site.
They have existing expectations for how that feature should work, and where it should be placed:
in the upper right corner of the screen usually.
Jakob's Law can help us to understand why external standards are so important.
Jakob's Law states that, "People spend most of their time on sites other than yours."
If all of those other sites follow a consistent convention, but your site breaks that convention,
You're forcing people to learn something new.
There are times when breaking conventions can be worthwhile.
Maybe you just figured out a new and better pattern.
Just remember you're adding to your users cognitive load every time
you make them learn something new. So, you should only do it when it's absolutely necessary.
In most cases, it's best to maintain consistency, both internal and external,
to improve your products learnability.