What was your ""I can't do this, I can go no further"" moment and how did you get over it?

My first century (100 miles) bike ride. It was an event in Madison, Wisconsin and I had trained for months prior to this but where I live there are almost no hills, so even though I had a prior ride where I did 90 miles without too much trouble, it was nothing compared to the hurt I was in for. On top of that I had almost no experience with these types of events and quickly my gear became a problem my shorts weren't padded enough and my seat was the low-quality stock seat that came with my no0b bike, so about 70 miles into the ride my taint was on fire, and I had to occasionally walk just to give it a break. I got over it by walking about a ten miles on the route, and when I got about five miles from the finish I got back on and just forced myself through it. Only took about a day to recover, and now I do at least one century ride a year.