The constant refrain in society is that you have to believe in yourself and confidence breeds success.
While confidence can certainly increase your success, IMHO, this is putting the cart before the horse. People usually feel confident because they’re successful, not the other way around.
Using piano as an example - growing up, I noticed that many music students would go down one of two paths early on. Either their first debut performance was a success, and bred confidence “Yes, I’m a good pianist, music is something I’m good at” - and they’d get better and better - or their first performance (or first few) was humiliating and unpleasant, and the seed got planted in their minds - “I’m not good at piano, music just isn’t my thing” and they often quit piano after a short while.
Success begat success; failure begat failure.
Same with dating, for instance. People like to claim that “confidence is the most attractive trait a person can have” but how can any man or woman feel confident if they’re getting rejected all the time (and then they get even more desperate, which makes their vibe even worse)? You have to first have the affirmation from others that you are attractive in order to feel attractive (no ugly person can fool themselves into thinking they’re handsome or beautiful when society is a nonstop 24/7 feedback informing them directly or indirectly that they’re not.)
Ditto with academics, sports, anything else. How do you convince someone who’s flunked math all their life that they’re really in fact a calculus expert deep down and that math is really their thing? You can’t, unless by pulling off some amazing mental con-job sales pitch.
Now, of course, there are some people who are simply so dogged or intrepid that they are able to take 100 licks and keep on ticking. Some of the famous entrepreneurs-turned-CEOs come to mind. But they’re a rare minority. Most people who keep tasting failure in a certain area, will eventually be convinced that “This just isn’t my natural strength” and their lack of confidence will simply feed their further lack of success in that area.