The best and easiest way to be mentally tough when you race is to get through training that requires the same or even greater mental toughness.
If you are someone who regularly pulls the plug in training when it gets hard or runs 45 minutes when the workout was an hour or does 25*100 when the workout was 30*100 then you stand less chance of really being there when it gets tough in races. If your default position is to jump ship every time it gets hard in training then guess what’s going to happen when it gets hard in a race?
So don’t be that person.
Be the person who shows up and does the work every day with discipline, integrity and intent.
Be the person that shows up with the best attitude every day.
Be the person that still has the best attitude even if the workout kicks your ass.
If you are that person over and over and over again in training- that’s the person that will show up on race day.