I think in alot of ways it takes more guts to pull out of a race than continue on.

often when we take walking groups on charity challenges such as the 3000ers in 24 hrs, they need to be told when they should cancel - they desperately don't want to fail but, as they stand there shivering from top to toe with the prospect of another 8-10 hours yet to go in driving rain, you need to let them know it's better to have the guts to get yourself to safety rather than blindly push on and have to rely on mountain rescue.