His younger brother, my uncle, was diagnosed with schizophrenia at age 20 after becoming severely erratic while away from home on an LDS mission. The diagnosis devastated their family, and has been followed by decades of difficult treatment and heartbreak.
What is it about my uncle that pushed him over the edge? Environment? Genetics? Pure chance? I wish I could know. My dad says that there's not much left of him except for a few moments here and there.
My dad had a big family, and he's said that his younger brother always showed the most promise, growing up. Smart, charming, super friendly. 30 years on he continues to greet everybody with a smile and hug, even if he doesn't know them!
It's sobering to see it in my own family, and it keeps thoughts like the one you articulated so well in the back of my mind constantly.