Like stress, a certain level of comparison is healthy, but go a hair beyond that and it quickly turns toxic. Comparison used as a tool to assign value is the real culprit.
So – what happens after mile 30? Does a secret door open up to a magical universe where fairies ride on the tips of unicorn horns, the secrets of life whispering forth from the flap, flap, flap of their wings? Nope. It was pretty much just more running and more pain and more joy.