I haven't been defeated yet, but I suppose it will happen someday. I do carry a mobile phone in case I need a bailout ride... I have a few friends (who drive by where I commute) who would probably relish that call.
My closest to defeat was one day I didn't eat much during the day, and it was I think the 3rd straight day of my commute.. I had no "emergency Gu" left, no bananas, nothing. I left for home, anyway. On the way home I bonked HARD. I suppose much of that was mental... I was passed by a guy on a rickety wheels-bent MTB. I felt like I should be riding a kids trike.
In other news... My trusty Light & Motion Solo died. The bike shop traced it to the battery. Odd, since it worked fine Thurs. and not Fri (I charged overnight). That was interesting... I push the button and... NADA. There it stand, in the pitch black. I sat around for awhile until it became a little lighter and then left.
My LBS gave me a battery to borrow while they ask L&M to replace mine. Big shout out to Roll on Polaris Pkwy for their excellent service!!!