Harvey turns in his report to the boss. Just a little behind schedule, but everyone is willing to put in some overtime. The following week every team member works 60 hours, and Harvey puts in 80. The first set of modules is done, but in the status meeting Harvey learns that the business rules aren't in the database, as they'd previously thought. They'll need to write a lot more code.
Nobody knows how much, but for now all bets are off.
His estimate was way off, he admits, and now he needs more programmers. He doesn't know exactly how many yet, he tells the boss. He has to run some new numbers through his estimate first. The boss will seek the OK to hire some contractors, but the overtime has already cut into the budget, so they might have to trim off most of the time budgeted for testing. Six Rules of Thumb Harvey fell into a half-dozen pitfalls.