"It’s been said that at 20, we worry about what others think of us and at 40, we don’t care what others think of us. As someone who has passed 60, my friends and I now realize that nobody was thinking about us to begin with. They were running their own run while we were busy trying to run theirs."

http://blog.rockmyrun.com/2014/11/28/whos-run-is-it/