Joel on software:
"When you think of writing code without thinking about all the steps you have to take, it always seems like it will take n time, when in reality it will probably take more like 4n time. When you do a real schedule, you add up all the tasks and realize that the project is going to take much longer than originally thought. The business people are unhappy."
Beat The Odds, by Joel Spolsky:
"Even when task estimates are done well, and they actually reflect the most likely amount of time that the task will take, you can't simply sum up estimates mathematically to get the project ship date, because when tasks go over, they go all this, using evidence-based scheduling and the Monte Carlo method, you can simulate your future schedule and generate a precise probability curve of possible ship dates that is far more informative and accurate than you get from naïve methods."