I remember reading project management literature in the early '90s, and really enjoying the works of Tom Gilb. The thing that sticks out the most in my mind is Gilb's Law:

Anything you need to quantify can be measured in some way that is superior to not measuring it at all.

Programmers are fond of saying "you can't really measure that," and Gilb's law says that's just a cop-out -- it might be hard to measure, and the measurements might not be 100% accurate, but anything is better than nothing!

It's hard to argue with that (and I don't really intend to). But like so many simple, absolute statements, it hides a lot of messy complexity. So much complexity that you (or your project) can fall into it and drown. There are three big traps lying behind Gilb's law.

1. Difficulty equates to cost. People have to work to get those measurements, the procedures may hurt productivity, etc. And if the measurements are of low quality, do they really offset the cost? Gilb's law says that measurement is possible, and it's always better than not measuring -- all else being equal. But the cost of the measurement may nullify its benefit.
2. Whether you call it Heisenberg's Uncertainty Principle or the Hawthorne Effect, the result is the same: measurement nearly always has secondary effects. And they may or may not be desirable. Are the people on your team optimizing for the measurement? Is that going to help or hurt your real goal?
3. Finally: few people deal well with ambiguous numbers. No matter how many times you say that the numbers have a margin of error, or may reflect many other factors, most people look at measurements and behave as if they're absolute.

Gilb's law is a law, but when it hits the complexities of the real world, the result can be messy. Use it carefully.

Today, NASA is thinking it probably wasn't a problem with the insulating tiles on Columbia -- or at least, not one that was caused by the main tank debris that hit the shuttle on liftoff.

Nevertheless, the most disturbing thing to me about the whole affair is learning that, even if they knew there was a serious problem with the tiles, there would be nothing they could do. In such a case, I suppose there's always the chance of a rescue mission by one of the other shuttles or by a Russian craft. But you can also think of dozens of reasons why such a thing wouldn't be able to happen in time. So NASA says they didn't even do an EVA to check the tiles, presumably on the assumption that it would be better not to know. It's hard to argue with that, assuming that they really couldn't do anything about it.

I don't guess I'm really surprised by this. Working in vacuum and microgravity is difficult, and putting those tiles on is notoriously tricky under the best circumstances. I know they use a special adhesive, and who knows whether that would adhere or dry properly in vacuum, or in the cold? And maybe they have to be applied under high pressure. But even though I'm not surprised, it's very troubling to think about that situation: there's something badly wrong, and it seems trivial (missing tiles!), but the crew will die, and there's nothing they or anyone else can do.

It points to the next big challenges of spaceflight. Somehow we have to have a cheaper, simpler way out of the gravity well, so that we can have ships that are simple enough to be repaired in space. And we need to work on technologies that make it easier to work in microgravity and vacuum: lighter, less constricting and more flexible spacesuits, as well as thrusters or other tools that make it easier to get around, and ways to gain leverage in the absence of weight and friction.

(Oh, and I'll second what Rael said.)