Unpredictable. Unfocused. Just like life.

Andrew at Bound By Gravity lists some classic software mistakes. I've seen these a million times in almost as many companies. This is my favorite:

In Case Study 3-1, Bill had no reason to think that the Giga-Quote program could be developed in six months except for the fact that the company needed it in that amount of time. Mike's failure to correct that unrealistic expectation was a major source of problems. In other cases, project managers or developers ask for trouble by getting funding based on overly optimistic schedule estimates. Sometimes they promise a pie-in-the-sky feature set. Although unrealistic expectations do not in themselves lengthen development schedules, they contribute to the perception that development schedules are too long, and that can be almost as bad.