Critical Chain - Eliyahu M. Goldratt [49]
The class is silent for a long while.
I'm supposed to do my thinking outside class, here I'm supposed to teach. I break the silence. "Anybody want to comment on what Ruth said?"
Fred raises his hand. "There is something that bothers me from before. For the past half hour we've been speaking as if we agreed that people put a lot of safety into each step. I'm not sure about it. I've checked some numbers, and they don't support that conclusion."
That's interesting, especially coming from Fred. "Share it with us," I say.
"In our company we keep records of when each step started and when it was completed. I used the data to compute the elapsed time of the steps, and I compared it to the original estimates. Do you know what I found?"
He waits a second or two, then tells us. "I found some steps, very few, for which the elapsed time was shorter. Now I understand that it might be a result of people's reluctance to report an early finish. It also solves another problem that I had, estimations that are too accurate. Now I understand why almost half the steps were reported finishing almost exactly on the nose.
"What bothers me is what I found for almost a third of the steps. For this large group I found that the elapsed time was about ten to twenty percent longer than the original estimate. If there is so much safety in the original time estimates of each step, how can we explain it?"
And he continues. "Everything that I've heard so far can, maybe, explain why the safety does not protect the completion time of the project. The safety is wasted in the connection between one step and another. But what I'm talking about here is that I haven't found the safety that is supposed to protect the performance of each step."
"That's important," I say. "It means that if we don't have a mistake in our logic, it must be that we are somehow wasting the safety, not just on the project level but on the step level as well. Anybody have an idea?"
After a long while, Tom raises his hand. "Maybe we just waste it?"
I'm eager to encourage more students to speak up, so softly I say. "So it seems. Can you give an example?"
"Our assignment for today."
I don't see the connection. But Charlie does. "Tom is absolutely right."
For those who didn't get it yet, and that includes me, he explains. "When we got the homework assignment we all claimed that two weeks was not enough time to do it. And we succeeded in getting a postponement. Now how many of us, after we screamed that we needed more time, went back and immediately started working on the assignment? I bet that no one did."
Tom nods his head.
"The students' syndrome," Brian says. "First fight for safety time. When you get it, you have enough time, so why hurry. When do you sit down to do it? At the last minute. That's human nature."
Fred jumps on the bandwagon. "Only once we start the work can we find out if there is a problem or not. If there is, we start to work frantically. But we have already wasted the safety, so now we are going to be late. Yes. This can explain why, in spite of all the safety, so many steps finish a little late."
"Very good, Tom," I say. "It seems that everybody agrees with you. Based on personal experience, me too."
"I hate to spoil the party," Mark says in his deep voice, "but I don't agree. What Tom says exists, but not always. And definitely not when we are under pressure."
Then he adds, "I went over the steps Fred checked. I can tell you that in many cases that he checked, people were working under pressure. For example, many of the steps that took longer than estimated were done in the digital processing department. That department has been under constant pressure for years. Believe me, they don't waste time."
I look at my watch. Only ten minute left. If I want to finish this