>anyone can do it with the right mindset
Those are contradictory, I would guess the right mindset is one where failure doesn't destroy you to the point you get institutionalized.
Here is my stupid advice (won't work, it's a case of someone who knows less giving advice to someone who knows more, I have never started a company or anything, but as Gandalf said "Why Bilbo Baggins? Perhaps it is because I am afraid... and he gives me courage."): Buy a copy of a souls game (Dark Souls, Bloodborne, Sekiro, Elden Ring), play it with no summons and no over leveling, you'll eventually get to a difficult boss that will kill you many times, now the first Souls game I played was Bloodborne and I just gave up after a week, came back then gave up, came back again and it clicked and now they're my favorite series of games, I died like 50 times against some bosses, it would drive anyone crazy, the stupid mistakes I keep repeating, the unfairness of some of their moves, etc. doesn't matter, I chose to play the game and it's just a game so why get affected?
This will obviously not help you in anything related to startups, but it's a light way to learn to accept failure, is it the same kind of acceptance? I don't know...
Also you failed, maybe you're just 5 feet 6 and can never ever become a professional basketball player no matter how hard you try, does it mean you're less of a human being to the point you get institutionalized for it? of course not, you tried, you failed, maybe the 4th time's a charm, maybe not, if you become comfortable enough to try again without affecting your mental health sure, if not don't try again, a decent job, a family, a couple friends, couple hobbies, and you can live a meaningful life and maybe even be happier than many people who succeeded at what you tried.