Petroski: value of failure

Q: You mentioned the historical record, and in your books you write about a 30-year pattern with bridge collapses. Describe that. People have studied bridge building over almost a century and a half or more, and it’s been well-documented. They have noticed that there is a major bridge failure about every 30 years. The question is, why 30 years? One of the explanations is that this is about the duration of a professional generation. An engineer’s career is about 30 years long, roughly. What happens is that these young engineers are coming in and the older engineers are, at the same time, moving out. The older engineers have all this wisdom and experience. But many organizations don’t have a formal procedure for taking that knowledge that’s in the older generation and imparting it to the newer generation. Or even if they do, the younger generation is sort of cocky and thinks they know more. After all, they’ve just gone through school and they’ve learned the latest stuff. So even if there is an attempt to pass on the wisdom to the younger generation, the younger generation either rejects it or doesn’t take it very seriously. Then the younger generation, depending on where it comes in the cycle, if it doesn’t experience failures directly due to its own miscalculations, it gets cocky. It gets comfortable, overconfident and complacent, and all of those qualities welcome mistakes and they lead to failure   (Interview with Henry Petroski, reprinted at Q-ideas)