Health. At my advanced age, first it was to save my knees while still allowing me to continue rides that involved a lot of climbing. A later diagnosis of Myasthenia Gravis meant e-assist was the only way I could keep riding, as I can kick on the motor when my muscles give out. While e-assist is fun and a great environmental alternative and there are lots of other non-medical reasons to have one, I feel really fortunate that I live at a time when it's an option for those of us who couldn't ride without. The thought of not being able to ride at all is really depressing - I know you understand. As long as i can ride, I can deal with anything. It's mental as much as it is physical.