The next piece of software is to be developed by 2 teams and they now have to answer how long it’s going to take. Team A says 5-8 months and Team B 6-9 months. But the department head is under pressure to deliver a date, so he takes 7 months as the average of the 2 teams. In this talk I will explain why average-based plans fail on average, then take a look at the psychological problems we humans have dealing with probabilities as a possible reason why we keep falling into the averages trap. Finally, I will show a way to avoid it when it comes to software development estimates.