Idk what your society or definition of “insanity” is but assuming you’re asking what we believe most commonly leads to one’s mental health entering a negative feedback loop:

Broadly speaking it’s some form of hopeless desperation (yes, the hopeless qualifier matters here) that commonly kicks into high gear after falling into homelessness, at least based on my own observations

Some also get to play on hard mode simply for winning the genetic and/or socio-economic anti-lottery