Whatever we are working on, mulling over, avoiding, contemplating facing, or rehearsing in our minds becomes literal. It’s you and the thing and the thing becomes the hill and there you are — taking it on. There is a certain amount of clarity that oxygen deprivation provides. Couple that with pain and you get the inner hum that becomes white noise and suddenly you can think.
Kristin Armstrong, Stones, Mile Markers blog, Runner’s World.com