Dumbing down analogies aside, you can look at software development as a graph of connected tasks with each task having some variance around when it would comple

Dumbing down analogies aside, you can look at software development as a graph of connected tasks with each task having some variance around when it would complete. This variance accumulates as taskw are completed and you move on to next nodes in the graph. When you complete the graph, you have large probability distribution about average ETA. Most decision makers have to choose some number for ETA however because world does not understand probability distributions or variances. Most likely this has to be lower end of the number to get project sponsored or fend off the competition. This is not unique to software development. Any projects that requires large connected graph of small task nodes would show same characteristics. For example, fighter jets, Boeing Dreamliner, space station etc etc.