Project Management Triangle aka The Iron Triangle

Episode 79 - 05 Apr 2017

Today's episode goes right back to one of the fundamentals of old skool project management:

The legendary "Iron Triangle".

There's a good chance you've never heard of the Iron Triangle: I've rarely heard it mentioned in the context of Agile.

Does it even apply to Agile? I'd love to know your thoughts.

Oh, and be sure to watch to the end for news of the newly-updated "Waterfall vs. Agile Cheat Sheet". Better still, grab you copy now.

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.

Welcome to Development that pays

Cutting-edge strategies for profitable Software Development

My name is Gary Straughan.

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.

I think that makes sense intuitively.

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.

looking around the room,

Taking some measurements

Scratching his chin

And saying

"I can do Fast, Good, and Cheap."

"Which two (pause) would you like?"

This "pick any two" thing is easier to see if I make the blobs overalp

Notice the gap in the middle. This indicates that it's not possible to fix all three parameters.

But it IS possible to fix the parameters in pairs.

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. OK?)

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 costs more money. Not ideal.

What if it costs less money. Oh, you'd be okay with that, would you.

What if it takes longer than a year. Not great. What if it's complete in 6 months. I'm sure you'd take that.

What about Scope?

How would 3/4 of a bridge work for you? What about 1 1/2 bridges?

You're right: both are silly.

We're going to need exactly one bridge

So the SCOPE is fixed.

In theory anyway, the cost and time parameters are viable for a Waterfall project.

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 the PM teams to most important:

  • Is time more important?

  • Is money more important?

Let's move on to Agile.

It's not immediately obvious that the Iron Triangle applies.

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 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.

So what are you waiting for - grab it now!

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Thanks for watching and I look forward to seeing you next time.