There are various versions of what Twain said or didn't say in this regard. Whichever version you choose, I can subscribe.
Loss of mobility is grievously annoying. I have lost most of the use of my left side. This is usually result of a stroke, but in my case, is a peculiar infection. I have weakness and lack of balance on that side. I can't walk unaided.
Also grievously annoying is that I can barely type. My left hand is my "typing hand," due to an injury to my right hand years ago. I have lost "fine motor control" in my left hand, which means my typing is erratic and slow -- not an ideal combination. That probably precludes my writing of my autobiography, even though it wouldn't be very long anyhow.
I am well cared for by daughter and granddaughter, plus Ladyfriend on weekends.
All is well, except my attitude, which is really crappy. I start physical therapy on Monday, which I am really looking forward to.
"This, too, shall pass." Just not fast enough.
Y'all keep up the good work, and