I've worked on 21s before. It's my understanding that there are multiple theoretic reasons for using Fibonacci numbers: * The bigger they get, the further apa

I've worked on 21s before. It's my understanding that there are multiple theoretic reasons for using Fibonacci numbers: * The bigger they get, the further apart they are. That is helpful because estimating big things is less accurate than estimating small things. * If the estimate gets to big, the next step is to split the task. Humans tend to err towards splitting things 50/50 (? I don't have an actual source for that) so it's generally more helpful to split a task into a slightly smaller and a slightly bigger subtask. Fibonacci numbers make that very easy, and recursively possible.