The diagram below is Figure 4.1 on page 62 of my new book Managing Projects as Investments: Earned Value to Business Value. It is a Google Books Ngram Viewer graph. It shows the number of times, year by year, from the set of five million books that Google had digitized through 2008, that the terms “critical path” and “project management” were used. It shows that both terms started being used just before 1960. “Critical path” shot up much faster, but peaked in 1968. Thereafter, despite the fact that “project management” continued to rise for decades, surpassing “critical path” in 1980, the usage stats of “critical path” first fell from the peak and since then have remained moribund.
Figure 9.1: Google Books Ngram Viewer graph for “critical path” and “project management” terms
Why is this? How is it possible that, despite the explosion of project management, the term for the factor that determines the length of every project (whether or not scheduled using CPM!) has failed to increase in usage?
I genuinely am asking this question because I am not certain I know the answer. I do have some ideas, however.
The first is the fact that critical path scheduling takes effort. As 2002 Nobel laureate in Economics Daniel Kahneman points out in his book Thinking, Fast and Slow, the hard work of computation and analysis require effort that people often find painful: what will happen first? What’s likely to happen next? How likely is it? What if a less likely event occurs? What contingency should we plan? And will we have the resources for that contingency?
All this planning, analysis, and other sweat-inducing labor, which are required behaviors for project management competence on any but the simplest projects, can be hard even to learn how to do. And actually putting it into practice is even harder. It’s a lot easier to say: “We’ll go with the flow and react to what occurs.” And that’s also a lot easier to do — until actual events blindside us and utterly destroy the project!
Part of the problem is that many people don’t understand the purpose of critical path scheduling and why it’s such a valuable technique. The assumption is that if we aren’t certain exactly what is going to happen and how long every activity is going to take, then the plan will be worth little.
There is an old project management adage:
Q: “Why do we put so much time and effort into planning the project?
A: “Because when we do, whatever we have planned will have eliminated ONE of the millions of ways the project could actually go!”
But there is truth deep in that tongue-in-cheek Q & A. The reason we plan is not because we expect the project, especially a complex project, to roll out exactly as planned. Things are bound to change during execution, and often in unexpected ways. Components will fail and require rework; expected resources will disappear; activities will consume their float; and the planned critical path will migrate hither and yon. But the project manager who has utilized the standard techniques of project planning will cling to the neck of that bucking bronco, spotting the variances, measuring them, predicting their impacts and alleviating the damage.
To briefly illustrate how critical path scheduling provides the project manager with the reins to maintain control of the project, let us take the simple network diagram shown below. We have performed the forward and backward passes and computed total float and drag for each activity. Now the project starts and the variances start hitting;
Figure 9.2: Critical path network showing early and late dates, total float and critical path drag
- D takes 12 days – what is the impact?
The project becomes 2 days longer. F, I, H and J all slip their early dates by 2 days. TF on B, E, G, K and L all increases by 2D. Drag on F increases by 2D to 9D.
- In response, we shorten F from 15 days to 9 days – what is the impact?
The project is shortened by 6 days to 66 days. TF on B, E, G, K and L all decreases by 6D. Drag on I decreases to 3D (now parallel with G whose TF is down to 3D).
- Finally, we discover that, by adding $100K in resources to Activity I, we will be able to shorten it from 20 days to 12 days. What is the impact?
Since Activity I now has only 3 days of drag, the project will be shortened by only 3 additional days, to 63 days. The critical path will migrate through Activity G. Is the $100K expense worth it?
No matter what changes hit the project, the project manager can see and assess the impact and perhaps find alleviating measures. This is what using critical path scheduling in planning a project can do, whether for 12 activities or 12,000 activities. This is what all project planning using traditional flexible techniques like WBS, CPM and resource leveling is designed to do: help keep that project from getting out of control. And those who fail, through ignorance or laziness, to use these techniques deserve to have their projects reap all those whirlwinds.
For other exercises in computing critical path information and critical path drag, see the exercises tab on this site.
Fraternally in project management,
Steve the Bajan