I, unhappily, have that understanding

So, you see, I really can understand how Sgt. Bob felt. There have been days when I've felt the same. I'm not suicidal at all (I have a very strong religious prohibition against it to sustain me), but there have been bad pain days when I've understood very clearly - experientially! - why some decide to check out rather than carry the burden any longer. I've never taken that step, and please God I never will: but I'm here to tell you from personal experience, pain can come to dominate your outlook on life to the point where it removes almost all hope, unless one has a very strong will to live. It's no surprise to me that many people in that situation say simply, "I've had enough. I can't take any more." Sgt. Bob was far from the first to make that call, and he'll be far from the last.
Mine was not nearly as bad a situation as theirs.  I had a back problem going on two years ago that was bloody awful.  I had the knowledge that there was a good chance of fixing things, or at least making them better, and in the near future, and it was STILL bloody awful.  When it won't let you sleep without meds, and getting up required two or three tries and a fair amount of cursing and screaming... oh, it's bad.  To be in that situation and see no improvement to come, just this every day and night for the rest of your life... I understood intellectually before this, that people could hit the point of "I have to stop the pain!" and kill themselves, after that it was more than intellectual.

And yes, one of my nightmares is that the problem will flare up again.  That's one flat horrible thought.  Should be treatable the same way if it does, but it would still be nasty for a while.  Funny thing to be able to think of that as somewhat of a blessing.