I have recently been enjoying reading a number of articles written by autistic adults. These two articles address the reasons why people with autism behave in particular ways.
A cognitive defense of stimming (or why “quiet hands” makes math harder) – by Cynthia Kim at “Musings of an Aspie”.
We are not in our own world – Judy Endow from Ollibean makes some very insightful comparisons between assumed reasons for particular behaviours and the actual reasons.