When we try to predict how long a task will take, we are in danger of falling prey to the planning fallacy. This is the natural human tendency to underestimate how long your own projects will take and the costs involved. To give one of many possible examples, when a group of students were asked to estimate how long their senior theses would take if everything went as poorly as it possibly could, the average estimate was about 49 days. In fact, the average time it took the students to complete t...