For some people conscious existence is too burdensome, uncomfortable, full of anxiety, outright maddening or some combination thereof. You see this in everyday life too, albeit in benign quantities - watch a kid after you tell him he can do nothing for the next hour.
I had read Phil Katz's story before and I read it again today - it wasn't any less painful the second time around. I think if we were to debug it - there doesn't seem to be any one unmistakable conclusion, rather a combination. It would all depend on how severely one reacts to their emotional trauma. Some people are numbed, some are able to move on, some find healthy diversions in hobbies, people, achievements and some like Phil just plain fail to function well and have to resort to drugs and alcohol in order to run away from the living nightmare. I think at some point existence becomes rather more painful than death for some - that's the only way you're able to kill yourself without regard.
Humans are puzzling as a species - all the years of conditioning, the everyday conflicts and contradictions we have to face, the constant need for asserting our existence through external means, the need for relations, the child/parent and then spouse systems and all the things that can go wrong with them, all the other uncertainties - amazingly many live through this but some just can't escape the dread.
Your comment reminded me of an essay George Scialabba wrote a couple years ago, "The Endlessly Examined Life" , where the author gathered over 40 years of mental health records from his therapists (mostly seeking treatment for depression and anxiety), unable to draw a real conclusion
>I am as puzzled and frustrated by the above records, and by the rest of my psychiatric file, as any casual reader could be. So much earnest effort, so much expert knowledge, so little success. The world’s most common disease is still this opaque.
Having read half a dozen compelling depression memoirs—Styron, Jamison, Millett, Solomon, Kaysen, McMurtry—I was skeptical, when The Baffler proposed publishing extracts from my file, that there was much more to say. Maybe there isn’t, at least not in that register. But maybe it’s enough just to keep talking.