"Suffering is the sole origin of consciousness" - Dostoevsky
Anyone who runs all night in California is going to have some good stories to tell, and I finished this entertaining read in 2 days. But read Ultramarathon Man for more than the funny anecdotes about pizza delivery in the middle of the night on a lonely highway. You'll want to find out what drives Dean Karnazes to run so far (up to 200 miles) and in such heinous conditions (at the South Pole, Death Valley, and so on). He can't exactly put his finger on why, or explain it to you if you ask him on the street, but anyone who reads his book will finish it with at least a sense of why he does it.
Chapter one, in which Karnazes tells you his insanely low body fat percentage, while eating a large pizza and cheesecake, while running all night before going to work the next morning, can be irritating. But hang on, because it's the ordinary, pre-endurance running years of the author's life that makes his story inspiring. He wasn't born superhuman, and he isn't even a pro athlete now. After a certain number of miles, he tells us, it isn't your body that makes a difference, but your mind.
If you end up liking Ultramarathon Man and want to read more, try Lynne Cox's Swimming to Antarctica. Cox is an endurance swimmer and her book is longer and more literary if I remember it correctly, but her life story is eerily similar (California kid grows up to tackle Antarctica/ungodly distances).