I spent about 3 years volunteering at a mentally disabled people charity: its mission was to try and help through sports, basically leading workouts at different levels in a large gym in the winter, and at a track & field track in the summer, in order to help them burn some energy and feel better in general.
It gave me a much stronger appreciation from having been lucky enough to be born without genetic impairments, and exposed me to a lot of very harrowing situations. The one I remember most is probably one where the son had some sort of progressive genetic condition where when he was young he was fine, but over the years he was losing more and more functionality (speech regression, physical control regression) he was in the mid-late stages of the disease when I was there and you could see his father remembering how he was earlier, and trying to cherish the current state of his son, while knowing what was to come and that he was going to lose him.
I think everybody who talks about "pulling oneself up by their bootstraps" and "anybody can do it via hard work" would benefit from seeing that unfortunately we are not all born equal, and that you can work as hard as you want but if you're not lucky enough to be born with the right body, in the right place at the right time, it won't mean much. I remember there was a friend of a friend that came by sometimes, he didn't have a mental impairment at all (he was super super sharp, and wrote amazingly well, I think he was actually published) but he had little control over his body (stuck in a wheelchair, drooling, could not talk at all) and was able to communicate via a jury-rigged typewriter since he was able to more or less move one hand. He definitely understood very well what was going on and his predicament, but he was still able to make something of himself and (mostly) have a positive attitude.
When I see all the sports people that say "I succeeded because I wanted it more than my competitors and I worked super hard for it", it makes me think that quite a few of the people I volunteered with worked super hard to run with significant impairments that made their gaits anything but normal, and week after week they would train to get better, but obviously they would never win a marathon or anything. Every elite athlete when asked first thing should say "I am so extremely lucky to have been born with my genetics, I worked hard, yes, but so does everybody else"
And dovetailing on what I was saying above: I also was shown time and time again that just because two people have the same disability, it doesn't mean they are the same, or that they want the same things, or that they need the same things, a significant disability sometimes makes you not see the rest of the person, but they are still there.
It definitely was a very important experience in my life, and definitely very recommended for everybody. I made quite a few friends while I was there and many years later I still wonder what happened to them.