clipped from www.37signals.com

Here’s the problem: You agree that feature X can be done in two hours. But four hours into it, you’re still only a quarter of the way done. The natural instinct is to think “but I can’t give up now, I’ve already spent four hours on this!”.

So you go into hero mode. Determined to make this work, but also embarrassed that it isn’t already so. So the hero grabs his hermit cape and isolates himself from feedback. “I really need to get this done, so I’ll turn off IM, Campfire, email, and more for now”. And some times that works. Throwing sheer effort at the problem to get it done.

But was it worth it? Probably not. The feature was deemed valuable at a cost of two hours, not sixteen.