I am a professional software project estimator. While not blessed with genius, I have put in sufficient time that by Malcolm Gladwell’s 10,000 hour rule, I have paid my dues to be competent. In the past 19 years I have estimated over 2,000 different software projects. For many of these, the critical inputs were provided and all I had to do was the modeling. Other times, I did all of the leg work, too: estimating software size, determining critical constraints, and gathering organizational history to benchmark against. One observation I have taken from years of experience is that there is overwhelming pressure to be more precise with our estimates than can be supported by the data.
In 2010 I attended a software conference in Brasil. As an exercise, the participants were asked to estimate the numerical ranges into which 10 items would fall. The items were such disparate things as the length of coastline in the United States, the gross domestic product of Germany, and the square kilometers in the country of Mali: not things a trivia expert would be likely to know off hand. Of 150 participants, one person made all of the ranges wide enough. One other person (me) got 9 out of 10 correct.