Mental toughness is a pretty vague notion, but if you're talking about driving yourself relentlessly to a goal, then I've got that by the boatload. All my life, I refused to be a quitter. If I settled on a goal, then I wasn't stopping - period - no matter how unpleasant or prolonged it would be.
Unfortunately, that didn't automatically make me a winner.
Really don't know where it came from. Was I born with it? Or did it develop out of the massive frustration I felt in life? Can't say.
In college, my major was physics. I would not give up, I would get it. Somehow, though, I was flunking courses and barely got the diploma.
I was sick and tired of being a puny weakling and determined to get strong or bust. So I went to gyms and kept lifting and kept lifting and kept lifting. I read the books, paid for training, got blood tests, went to nutritionists. And after 30 years of killing myself, I'm still stuck at beginner's level. The only thing I can say is that if I hadn't trained at all, I'd be even worse.
I have one thing in common with Matt Kroc; I absolutely cannot stand losing. Unfortunately, other people keep beating me, so it's unbearable.
Matt Kroc thinks mental toughness made him a champion. Well, he's partly right. Constant training unleashed his potential. But you need potential in the first place. Persistence will only take you as far as you can go.