What's your "why"? Why do you do what you do? What drives you? When it's time to grind, time to suffer, what is your reason for digging deep?
I think mental preparation is the most overlooked aspect of getting an athlete to the starting line of an Ironman ready to do his or her best. So many athletes and coaches focus on all of the tangible aspects of training and racing, that one of the most important but critical and somewhat intangible components. It's very important to have your watts, heart rate, pace, calories, fluid intake, electrolytes dialed in for race day. You also need to get to the start line with fresh legs. But none of those things matter a lick if an athlete cracks mentally when the going gets tough. You can be the fittest and fastest person on the start line, but if you walk because you're mentally tired or weak, you'll never reach your potential as an athlete.
As a coach, one of the first things I ask my athletes to do is to think about and write down their "why". Why are they doing this? If you don't know your reason for being there, you will never be able to grind. It hurts too bad to be able to go on in hard training or in a race. That "why" is what will keep you going when it hurts really badly.
I rarely come up with ideas on my own. Back in my engineering previous life, we used to say "NIH", Not Invented Here. Don't try to create something that's already been thought of by someone else. The same goes with your "why"; I didn't come up with it myself. I love the motivational speaker Eric Thomas. He talks a lot about knowing your "why" and that it needs to be deeper than you. I think this is very powerful. If your reasons for racing Ironman are surface deep like "I want to go faster or get a PR time" when the going gets tough, it may not be enough to overcome the demons that creep in your head.
If your reasons for doing this are deeper than surface level, if you truly believe them, they're internalized, and if you can call on them on race day or in training when it's extremely painful, then I think you are more likely to keep going than to quit. It's too easy to start walking deep in the marathon. If you are doing this for your spouse or your children, If you can focus on the sacrifices they've made for you, a little pain isn't too much to overcome. You need a reason to get out of the "poor me" mentality during the hardest parts of the race. Our brains will try to get us to stop, but you need something deeper to get out of your head. I find something in your soul will trump your head. Some people can do this naturally. They have an innate competitiveness to be able to keep digging when it's hard. Others don't, but I think it's something that can be learned by anyone if they focus on it. This all starts by asking that question of "why". From there, start digging deeper into your own psyche and heart. You will find the answers that are specific to you. If you can find those, then focus on them every day, you will find that next place you can dig to on race day.
There are so many talented athletes out there who never realize their potentials because they overlook all of this. Watch an Ironman sometime… Stand around mile 16 of the run and you will see the people who have found that will within and those who are mentally defeated. Sure many people have to slow down because of physiological reasons like cramping, over-biking, under training, or nutritional mistakes. But you will see those who have just given up digging deep. You will also see those who are continuing to dig. They know their whys and are using when to drive them forward.