Elon Musk knew the chances of failure. He also knew the chance that he would succeed. The potential chance at success outweighed the potential loose from failure. That was my equation as an entrepreneur. I knew it was possible I would fail but the upside of success drew me in regardless.
You don’t hear about these people as few people push much past 100m unless wealth or fame is inherently a goal.
This means don't be over confident, but also don't be under confident.
But absolutely don't believe your chances are great for no reason as the self-esteem enthusiasts would tell you. I see countless people wasting their life away chasing ideas just because their self esteem is way too high. Don't do that.
If I remember correctly, Musk even had the mindset of "I will probably fail, but something good will come out of it, even if I fail". I think the details on this mindset matter on the "believe" part.
The quitters, of course, get nowhere.
For example Elon Musk very well knows the possibility of failure. But it seems he finds it important enough to try it.
Same for Jeff Bezos, who has a regret minimalization strategy.
So seems they are very aware of the possibility of failure, but it's important enough to try it.
I like that, because it's a more rational approach than "I'm sure I can do it"