It doesn't matter how great of an athlete you are, whether a casual runner, serious weekend warrior like myself or an elite level professional you will experience times in training and competing when the struggle is very real. You might be dealing with pain, discomfort and doubt in your ability which is just a natural part of putting massive effort into a physical goal.
I've witnessed myself pack it in during a race convincing myself that that ache in my hips was more serious than it really was, that I wasn't in good enough shape to overtake the runner in front of me or that the race wasn't worth it. After reading several sports psychology books and ones related to business success I decided to develop a short mantra to repeat to myself when the going became hard during training or a race. I also use it when I feel like skipping a workout as a means to remind myself how important my goals are for me.
The mantra I repeat to myself is "You either want it or you don't." I believe it's important that the mantra you choose actually means something to you. It should also be short and easy to remember, no long paragraphs of random thoughts. For me these words remind me that I'm showing up (being present & on task) and choosing to pursue my goals. If at some point I no longer wish to compete at running the whole mantra becomes irrelevant. But if I do have a desire to push myself and attain goals then it's decision time. If things are hurting during a race I just need to consider if this is truly important to me, do I indeed want it, and if so it's time to work for it. My mantra reminds me of that decision, and usually leads me to where I need to be mentally.
I'm not going to lie, this whole concept has had mixed results. There have definitely been times when I've pushed myself out the door on a cold wet day (or in particular into the gym, my least favourite type of workout) for a training session I don't feel like completing. I've been out running, feeling short of breath, a dull ache in my calves and began to run my mantra through my head and it's given me purpose and the means to push through. But there have also been times when I've popped my mantra though my head and still underperformed or chosen to dial back my effort. I just hope (wish) that having a mantra or purpose pays off 35km into a marathon.
Developing your own mantra certainly isn't going to hurt. Hopefully it is the one little habit that pushes your performance over the edge. The only caution I can offer is that if you start using it to push yourself to perform when you shouldn't (maybe during an injury) then it isn't serving you well. Provided the words are meaningful to you, it might just work to your benefit!