Last October I tried to run the Cappadocia Ultra Trail and it turned out to be the first race that I didn't reach the finish line.
There were a few reasons behind that and a few lessons to be learned.
Give your body proper rest after a (or a couple of) big races. I ran the Eiger Ultra Trail E101 in July and the Swiss Irontrail T81 in August. Looking at my training diary there is a significant difference between the amount of training I had prior to the Eiger (April, May, June) and before the Cappadocia Ultra Trail (September, October). During summer I had a massive goal of getting all qualification point for UTMB and I trained so hard for it. In late August just after the Irontrail, I was quite week and need a good recovery. I didn't run for a few weeks. Then I start training only a few weeks before the race. But the amount of effort I made was nowhere near what I should have. I should have respected my body more and gave it a good rest.
Never Underestimate a race. After this DNF, I'd never underestimate a race again. 110 km is not a short distance to be underestimated. What made me thinking it was easy, was the elevation profile. Although it was 9 km longer than the Eiger, the elevation change was almost half of that. So I thought it won't be a problem finishing this race -- and it wouldn't been so if I trained well. There were no massive ascent comparing to the Eiger, but there were some technical parts with no path and you had to climb the mountains.
Know where you are racing, get as much information as possible There were also some problems with the course marking and because it was a small race, you could easily get lost. In terms of support it was not quite efficient either. In my previous ultras, there were medical tent next to food stations and there were some volunteers along the way, especially during night to make sure you pass different areas safely. The organizers made a good effort during the Cappadocia Ultra Trail, but given that it was its first year running some issues seems to be inevitable. I might have finished the race and pushed myself further if I was sure about the support along the way.
DNF hurts. When it happens, do try to accept it. So if you find yourself in a situation that going on might cause severe damage to your health and keep you away from training for a while, it's better to give up and come back stronger next time. It does hurt a lot. It's more difficult to convince yourself to give up than dragging yourself to the finish line. My left ankle hurt a lot after 41 km and I eventually gave up at 77 km when it got worse and I also experiences hypothermia. I could probably endure the pain for the rest of the race, but it could weaken my ligaments badly and I did not want to be away from running for months. As runners we tend to live outside our comfort zone, but we should know how much is to much.