Sometime in my late 20’s, I was playing a basketball league game and felt as quick and sharp as ever. I just couldn’t seem to shake my defenders and get the step on them though, and figured they must just be excellent defensive players. Then later I watched the game tape and realised not only was I slower in reality than I felt, or had been in my prime, I was no longer covering the same distance laterally, so the defender didn’t have to move as much to contain me. Reality check.