I was reading the above comments & I feel that people should definitely learn from a holy neshama like he had. I was around him from time to time in Chaim Berlin and Camp Morris.
Like sem20 said “Dovid was the perfect person to talk to when you needed to kill time, or to cheer yourself up”, but I did it for that and to give him chizuk. As was said, he NEVER showed any tzar from his inability to strive and think like others. Rather, he took every day at a time, thinking of how to make the world a better place. For those who know him from my yeshiva, you can usually find him in the coffee room having a geshmake schmooz before we went to seder. He always had a smile and said jokes to make people laugh which I think made him feel better. He was a chaver to many and a chizuk to all!