Several years back, on the second century ride I'd ever done (so still working out pacing, hydration, etc) the temperature got deep into the 90s with high humidity. At about the 80 mile mark, I would have been wise to make the call of shame and get a ride to the finish, but I didn't. I finished the ride, but I know that I never want to feel like that again. I'm much more conscious these days about extended time in what is, for me, excessive heat and humidity.