Mental toughness can be learned. You have to believe in yourself and you can do that with self talk. Your unconscious believes what it hears. You can lift yourself up by your bootstraps and fake it until you make it with the mental game. I'm sure there is plenty of information concerning creating a positive self image on the net.
The other thing has to be earned the hard way, seasoning. Nothing helps mental toughness like having been in the same situation or tougher before, the more times the better.
A personal accomplishment I am proud of, in my second season of competition I shot the first perfect score in the fifteen year existence of some pistol matches. At least several dozen better shooters had tried many times before me including Masters, Grand Masters, and a many time world champion. I realized halfway through the event I had a real chance of shooting a perfect score and I went to the end of the firing line in the dark between each stage pulling together my mental game. Maximum score was 600 and many a 599 and 598 had been shot, it was the mental challenge of a perfect score that had prevented six hundreds.
I played one game of barbox eightball for a truly ridiculous amount of money, what it amounted to was what I had to show for five years of hard work. I figured my odds at a little above 50/50 if I lost the lag but more like 75/25 if I broke safe and left plenty of clusters. I could outmove and handle clusters better than the other player. Still a matter of the mental game, and the pressure was far greater on me. Five years of hard work for me, part of an every six months deal for my opponent. That barbox eightball game took at least fifteen or twenty minutes. I won because I performed up to my normal expectations the same as if I were playing for a beer or five bucks.
The mental game is build on ego and experience. Some like more polite words but I am pretty blunt and ego suits me. It takes ego to believe you can beat the best in the world.
Hu