My trips are all repeatable in the sense that I’ll be able to go back and do the trip at another time if for any reason I have to bail. I clearly remember the first time I did the Black Forest Trail in PA. It was early in April and raining and after the third time that my feet slid out from under me in mud or leaves on steep downhills I decided to bail before I got hurt. My two friends (this was the first time I met them or hiked with them) bailed later that day as well. I guess this means that I’ve never hit the “regret” point on a trip.
I feel that it might be different if on “the trip of a lifetime” – something like the Te Araroa Trail in New Zealand or hiking to Everest Base Camp. In that case I believe all the external factors (money already spent, time commitment, training, etc.) would make it difficult to make a decision to bail when it should be made, which could lead to an epic trip failure and regret. I think the other factor that may push people to the point of regret is not wanting to disappoint a hiking partner or partners, whether the peer pressure is real or simply perceived.
Interesting question. I the corresponding question with this would be: What would make you regret a trip? As mentioned above, serious injury or death are certainly answers…What else?