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Understanding Critical Path via Ikea
Submitted by krossi on Wed, 08/01/2012 - 12:36
Whenever I’m asked to explain project management concepts, I’m always eager to do it. Not only do I enjoy sharing the knowledge, but I also enjoy doing it in a way that ties in to what’s going on in my life. What’s going on right now you may ask? A new house—and it needs furniture, so these days I practically live at Ikea. It’s burned in my brain. So when I was asked to explain critical path, I thought it would be a good creative workout to marry my love for Ikea with this all-important project management concept. What follows is the result: Critical Path Via Ikea.
Let’s say that one Saturday morning you drive to Ikea and buy a great coffee table for your living room. You get it home, open the box and see that assembly requires 8 steps and that each must be performed in order, one at a time. You estimate each step will take you one minute.
If you were to lay these tasks “end to end” visually, they might look like this:
When viewed in this manner, the tasks look a bit like a path, don’t they? Hmmm…
Anyway, you may look at these tasks and wonder which are on the critical path. The answer? All of them. Why? Because if any of them takes longer than expected, the project will go over its 8-minute ETA. When a task directly affects the project ETA (not just the task ETA), it’s considered critical.
“But”, you might say, “wouldn’t everything on all projects be critical? It all has to get done, right?”
Well, yes and no. All tasks do need to get done--but all aren’t necessarily critical. To explain why, we’re going to need more furniture. So let’s get you back to Ikea for a couch and a TV stand…
OK. Now you’ve purchased a couch and TV stand and brought them home. You open the boxes and see that the couch takes 5 steps to assemble, and the TV stand takes 10. And you still have your coffee table too. You estimate that all the steps are still one minute each, and you decide you’re going to do the assembly by yourself. Visually this looks like:
Where is the critical path now? Same place it was last time (i.e. the entire chain). Why? Because even though your project is bigger, you’re still in the same boat. If any of these 23 tasks takes longer than a minute, the project ETA will go over 23 minutes.
Again you might say, “Then everything on all projects is critical. It all has to get done.”
Not necessarily. Let’s go back to the living room and mix things up…
There you are in your living room surrounded by boxes and pages of assembly instructions, and suddenly you realize that you’re crazy to do all this assembly alone. So you decide to get help. You call 3 friends and invite them over, asking each person to assemble one item for you while you supervise. (Congratulations--you’re officially a project manager now.) Let’s revise our visual:
Now which path is the critical path? It’s the TV stand. Why? Because those are the tasks that determine when the project can end. Those tasks, taken together, create the outermost boundary. Therefore, they most directly impact the project ETA. If the TV stand takes only 9 minutes, the project ends in 9 minutes. If it takes 11 minutes, the project ends in 11 minutes. It’s a very direct relationship.
Now we’re getting somewhere because now we’re able to see how it’s possible for some tasks to be on the critical path while others are not. But don’t walk away yet. There’s a catch. The critical path doesn’t always stay in one place. It can switch around as a project moves forward. For example…
Your friend George is assembling the coffee table and is about halfway through when his phone rings. It’s his girlfriend. He says the call will only take a minute--but it doesn’t. It takes 6. Now what does the project look like? What happened to the project ETA?
That’s right—it’s 14 minutes now. And where is the critical path? Is it still the TV stand? No. It’s the coffee table now. And here are all the scenarios that can play out from this point:
- If the coffee table cannot be done in less time, then the project will extend. The new ETA for the project will be 14 minutes, and the coffee table is critical path all the way.
- If the coffee table can be done in 10 minutes, then the project ETA is 10 minutes, and the TV stand AND the coffee table are both critical path.
- If George works really fast and brings that coffee table down to 9 minutes, then the project ETA is still 10 minutes, but the TV stand is critical path once more.
Also, it is interesting to note that:
- If George’s phone call had only taken 1 minute, neither the project’s ETA nor the critical path would have changed.
- If George’s phone call had taken only 2 minutes, the project’s ETA would have remained intact, BUT the critical path would have switched to both the coffee table and the TV stand.
- Once George’s phone call hit the 3-minute mark, the project ETA started sliding out.
Surely you can see how this information would be useful in managing any project.
And that is the heart of critical path. In terms of day-to-day use, I don’t think of critical path as an expression of importance or even of time. I think of it as an expression of vulnerability; more specifically, the location of vulnerability. Vulnerability of what? The project’s ETA. And that, my friends, is Critical Path Via Ikea. I hope it’s been as useful and fun as a lipstick-red armchair.
Now, who wants Swedish meatballs?