I think it would be very useful to define processes by which entrepreneurs can better determine if they are hanging on too long. Processes that have more depth than just playing with numbers. Perhaps its simply soliciting more critical feedback from others at key points along the path?
It might be possible to set up some system that you can judge yourself by. Maybe a quiz that you can take every month that is developed by psychologists, entrepreneurs, and VC's with questions on your progress, motivation, financials, etc. Your score reflects your chances of success, and you can track it from month to month. That way you will see more clearly whether things are going well or to hell. It would be like with small children: If they are your own you don't notice how quickly they grow because you see them every day. People that only see them every month notice right away.
There is certainly enough "distance" between many of the participants here to get open feedback.