Mental Illness, Mental Strength and Philosophical Discourse The Anna Karenina theory might apply here: All happy people are alike; each unhappy person is unhappy in his own way. It's similar to the Isaiah principle: All we like sheep have gone astray; we have turnéd every one to his own way. Except Isaiah is more pessimistic: Tolstoy apparently thinks life works out quite well for a lot of people, even if not everybody. Isaiah find us all wandering into the weeds for different reasons.
So, what characterizes happy people? Are there commonalities in the ways we go astray?
My theory is that happy, mentally healthy, successful people are presented with no confounding factors early in their lives that are greater than they can understand and overcome. Unhappy and mentally unhealthy people have, conversely, been presented with confounding factors which they could neither understand nor overcome. Intelligence explains little here, because no matter how intelligent child is, he is too undeveloped to have the insight and information required to grasp his difficult situation. That won't come along for another 20 years, perhaps. By adulthood the unfortunate child has had plenty of time to develop some crazy features.
this doesn't account for all craziness. People with major mental illnesses (like bi-polar disease) are screwed from the get go, however happy a family they had, and no matter how well they navigated the ingravescent inimicalities of childhood.
Some of us didn't socialize well as children. We didn't fit into "the group". We were outliers. We were deviants in various ways. Because of our outsider status, (not always outside, but outside often enough to be very familiar with the experience) we failed to develop both social knowledge (how society works) and social skills (being able to move smoothly through society.
People who are touched by outsider--outlier--deviant status, tend (a tendency, not a rule) to be propelled further outward. They aren't propelled so far that they are actually outside, though. They live altogether within society, but without the full set of skills that belongers, conformers, and central tendency folk have. The outsider--outlier--deviant experience much more social friction than most people do, and this further alienates them, and it might not occur to them what is happening to and around them. Again, this isn't about intelligence, it is about an insufficient skill set, insufficient insight based on poor experience, and the like.
The resulting stress, sturm and drang, anger, disappointment, unhappiness, job loss, broken relationships, frustration, sorrow, loneliness, et al produce a good share of what is classified and treated as "mental illness". These people aren't crazy, exactly; they're just not very successful at life. Do drugs help this sort of problem? Sure, they help in as much as many of the drugs used for depression have a tranquilizing effect, and the tranquilization of an antidepressant is possibly (but not invariably) safer than any one of several well mixed cocktails--old fashioned, manhattan, martini, gin and tonic, etc.
We can add chemical abuse, debt, long and taxing commutes, and a lot of other crap that tends to make people feel, if not act like they are, to use a shorthand term, crazy.