Comments on _Critical Chain_, ch 9

This chapter's setting is the professor and his class again. They are talking about Gantt charts.

Then the professor asks about the critical path.

“The critical path," I remind the class, "determines the time it will take to finish the project. Any delay on the critical path will delay the completion of the project. That's why the project manager must focus on it."

That's what I had imagined "critical path" to mean as I was reading earlier chapters of this book. The points that are not part of the critical path are all the points that, if improvements or delays happened at those points, the whole project time doesn't change. (A long enough delay at a particular point could potentially change it from not being part of the critical path to being part of the critical path.)

Then they start talking about the non-critical paths and when it makes sense to start them -- at the earliest possible date or the latest or what?

Then someone suggests that it would be good to postpone the non-critical paths until latest possible date so that the project manager is not overwhelmed by too many things to focus on.

“Exactly," Ted bursts in. "So if we start everything on its late start, everything becomes important. And I'll have to concentrate on everything. Kiss focusing good-bye."

Yeah so if you start everything at it's latest start, then the non-critical paths become part of the critical path.

“Concentrating on everything is synonymous with not concentrating at all," I agree with him. "So where do we stand? If the project leaders use early starts, they will lose focus. If they use late starts, focusing is not possible at all. We have to find the mechanism, the rules, that will enable a project leader to focus."

moving on... 

“It's not long before we get a good handle on how progress is measured in reality. Not much different than what I found in the literature. Progress is measured according to the amount of work, or investment, already done, relative to the amount still to do. In all my students' cases, including the cases where milestones and progress payment were used, this measurement did not differentiate between work done on the critical path and work done on other paths.

ouch! what a bad way to measure project progress! it doesn't help anyone figure out whether they are on track to achieve goal success or goal failure.

“Can anybody predict the impact of measuring progress in this way?" I ask the class.

"We reward starting each path at the earliest possible time," Brian is quick to notice. "This measurement encourages the project leader to start unfocused."

"Moreover," Charlie notices, "it encourages the project leader to continue being unfocused."

"How come?"

"Because according to our measurement," he explains, "progress on one path compensates for a delay on another. So we encourage progressing fast on one path even though another path is delayed."

"What's bad about that?" Mark asks. "If I have difficulties in one path, why shouldn't I move on the other paths where I can?"

"At the end they all merge together," Charlie reminds him.

“All the advance that you gain in the open paths will have to wait for the delayed path anyway. You made the investment too early, and what is worse, you allowed yourself to not concentrate on the place you should, on the delayed path that needs your attention."

So the metric used incentivizes focussing on non-bottlenecks instead of focussing on bottlenecks.

This is similar to how people calculate an average by doing a non-weighted average when they should be calculating a weighted average. So like imagine driving from city A to city B at 60 miles/hour and then back to city A at 40 miles/hour and somebody asks what the driver's average speed was for the entire trip. Lots of people would say 50 miles/hour, incorrectly treating each leg of the trip with an equal weighting in the average calculation. If they correctly treated the 2nd leg as more weighted for the whole trip (since it takes up more time than the first leg), then they would have done a weighted average (resulting in a figure that is between 40 and 50).

This parallels the project management scenario in the book. Project managers are incorrectly treating each point in the path as equally weighted in determining goal success.