Not sure what to say here. I've done a few tris now and unless it's an Ironman distance race, you shouldn't be quitting. Especially during the bike segment, which has a very low risk of overuse injury on race day, unlike running. And, the bike is only the 2nd segment - you should have more than enough in the tank to hammer both the bike AND the run unless it's an ironman distance race.

In any case, including the Ironman, you should be well prepared to tackle the race at hand. It's ok to quit if you suffer an unexpected on-course injury, crash, or some bizarro environmental circumstance that makes going further very unsafe, but I consider quitting due to fatigue just bad planning. Even for first-timers - I've met many first timers who, with the guidance of a coach, rocked their first IM. (They trained a LOT as well.)

Chrissie Wellington is unparalleled. She dominates the women's section so badly that the women literally race for 2nd place whenever she enters - it's a bigger gap than Alberto Contador has on his road racing peers. (Probably by 2-fold.)