Off-hand? Algorithm driven social media, “news” media generally, politicians, family/kids. The last is at least usually tolerable, or at least correctable. The rest should be taken only in moderation with a mound full of salt.

Powerful people. People who have the money and the power are corrupt EVERYWHERE. Yet we ignore this and move on and pay and pay and pay.

concentration of capital and means of production in the hands of a handful of oligarchs exploiting the rest of society

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

Brutal school bullying from 80's to mid 90's and nobody giving a shit. Now we have middle aged people still broken and unable to function properly.

Lack of mental stimulation ( I would also add sence of acomplishment to go with that mental stimulation.) People like to solve problem and feel good about solving those problems. When you have nothing to engage your brain it turns to other things even when those things arnt real. If you do do things with your brain but you never get any reward for it you tend to look for more extream things.

money and leverage

Which society?

Trump

Your landed lord demands tribute in 27 days.

Neverending obsession people have with sex. Yes, I get it, it's fun, and adventurous, and all those other amazing things. Can I just enjoy the rest of my life now?