Mental illness is a complex entity. Beware of any simple "definition of insanity"

I recently discovered I have a mutation which makes my verbal intelligence too high to measure but has negative effects in other areas. Other people have similar variations.

Some kinds of mental illness such as schizophrenia seem very much to be a biological phenomenon, but stress and particularly the way stress is structured has a definite negative effect on the origin. You can become stronger and more capable in many areas by applying stress in the right way (athletic and military training, for instance), but stress without time to recover has negative effects on body and mind and certainly surplus coercion leads to surplus stress.