I'd also add the following things I've learned from hard-won experience:
- The vast majority of your training needs to be in Zone 2, which is probably a lot easier than you think. This is the only way that you can consistently maintain significant amounts of volume without breaking down physically / mentally. One of the most important things I learned while training for my first 50 miler, being completely broken down with injuries and having physios tell me that I was never going to get to the start, was to slow my training all down to Zone 2. At the start of the race three months later, I had logged more volume than in the previous 9 months and I felt great. I lost speed, but real Zone 2 training is bulletproofing.
- Dial in your hydration and nutrition. The temptation is always to train fasted or try to save costs of gels etc, but the benefit of knowing exactly what you need to take in on an hourly basis, and sticking to that (no matter how tempting the aid station Pepsi or Haribos or whatever are), is worth it's weight in the vomit / diarrhea that's not going to explode from your body as you DNF.
- Dial in your setup. My only real DNF came from a bikepacking race where I hadn't tested my setup properly and thought that, with all the training I'd done (and I'd done a lot) on a 12kg bike, I'd be fine on an 18kg bike. I wasn't. After a huge first day (260kms & 4000m on gravel, with lots of hike a bike), my knee gave up completely and I had to limp to the nearest train station and scratch. For my first 50 miler, I did a lot of running in *everything* I was planning to wear, down to the T-shirt, socks and cap, so that I knew that I could handle 15 hours of running.
