Originally Posted by
Sekhem
...I think the mental toughness issue is just the DECISION to finish the ride and everything else is irrelevant.
That's my take, too. Show up at the start with the decision made to carry on as long as possible, no matter what happens. There are times in the ride where you might easily bail if your heart and head were not in it. But, if you are committed, you push through, and things usually get better (then worse, then better again). If you are reasonably prepared, and don't quit, the odds are with you to finish.