Today we'll look at a stalwart of old school project management
The Iron Triangle.
And I have a new version of the "Waterfall vs Agile Cheat Sheet" for you.
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My name is Gary Straughan.
This is The Iron Triangle.
Forged in the fires of Mount Doom.
What's that?
We couldn't get the graphic?
What did you get?
Okay okay... we'll go with that.
The Iron Triangle
aka the Project Management Triangle
aka the Triple Constraint
has been around a long time.
The version I first came across was this one.
Time, quality and cost.
The three parameters are interconnected.
Change one and one or both of the other parameters change.
For example, if you want to shorten a project, you might
1.
Skimp on the quality
2.
Throw money at it
3.
Skimp on the quality AND throw money at it
Things get interesting when we fix one or more of the parameters.
My mental model for this is a decorator coming in to do an estimate.
He comes in, looks around the room
Takes some measurements
Scratches his chin
And says
"I can do Fast, Good, and Cheap."
"Which TWO would you like?"
Cheap and Fast ... rush the the job and the Quality will suffer
Cheap and Good... is going to take time
Fast and Good - which might mean putting more people on the job -
will push the price up.
And that is all you need to know about the Iron Triangle:
The three parameters are interdependent
You can fix one
You can even fix two
But you can never fix all three
We're ready to move on too apply the Iron Triangle to Waterfall and Agile.
And for this there's a variation of the Iron Triangle that's a better fit.
It swaps Quality
for Scope
(Actually, this is the more common version.
So if you're going to memorise one of them,
memorise this one!)
How does the Iron Triangle look for a Waterfall Project?
Which parameters are fixed, which are variable?
Let's see if we can figure it out.
We're going to build a bridge.
It's going to take one year and cost
one million dollars
cost: $1m time: 1 year
scope: 1 bridge
What if it goes over budget?
Not ideal.
What if it comes in under budget?
You'd be okay with that, I think.
What if it overruns.
Not great.
What if it takes just 9 months.
I'm sure you'd take that.
What about Scope?
How would 3/4 of a bridge work for you?
What about 1.5 bridges?
You're right: both are silly.
We're going to need exactly one bridge
In theory anyway, for a Waterfall project, SCOPE is fixed.
and cost and time are variable
it would be remiss of me not to mention that
most project managers will CHOOSE to fix a second parameter.
Which they choose will depend on what's more important:
More important to finish on time?
Or on budget?
Let's move on to Agile.
It's not immediately obvious that the Iron Triangle applies to Agile
For one thing, many Agile projects don't have a crisp start and a crisp end.
But I can side-step this problem by picking an arbitrary block of time.
Say, three months.
Let's look at the parameters
Time.
That's fixed.
3 months.
Cost.
Well, if we're talking about a software project,
most of the cost... is the cost of the project team.
Agile teams tend to of a more or less fixed size.
Fixed team, fixed time.
Looks like cost is fixed.
Time is fixed, cost is fixed.
By the rule of the Iron Triangle
this means that the scope must be variable.
And that fits with our experience, right?
And Agile team cannot
indeed should not
must not!
predict what it will be able to produce in a three month period.
They'll start work, they learn, they'll produce.
And at the end of the three months,
we'll get what we get.
Like I said: fixed time, fixed cost, viable scope.
There's a rather satisfying symmetry between the Waterfall and Agile Iron Triangles
I'll spin this around a bit.
Notice that:
- What's fixed for Waterfall is variable for Agile
- What's variable for Waterfall is fixed for Agile.
Perfect iron-triable opposites.
The Iron Triangle is just one element of the
"Waterfall vs Agile Cheat Sheet"
which has just received a minor make-over.
If you're one of the 200+ that received the first version,
watch your mailbox for the updated version.
If you've yet to grab a copy, you'll find a link somewhere around this video.
click the link, follow the instructions. and it's all yours.
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