Kipchoge has not run a bad marathon. I don't know his precise splits, but I'm guessing he has never run a drastic positive split. He has never "blown up." He appears to have run very smart and in control, in all of his marathons.
I'm worried that his sub two hour attempt will see him run on pace for 35k and then experience some sort of blow up. If this happens, will it take a long term mental and physical toll that he never fully recovers from?
I hope this isn't the case, but I'm worried for him. He is one of my favorite runners.