Self-confidence, or positive perception of self, improve the chances for success (assuming we define success as an overall condition of physical, mental, financial, etc well-being over an extended period of time), and might in the case of mental well-being be required for it. But as Shakespeare wrote in Twelfth Night, "Be not afraid of greatness: some are born great, some achieve greatness and some have greatness thrust upon them."

There is no doubt that some people are born great, even if environment plays a significant factor in their developing greatness. Intellect is largely genetic in basis (during my educational psychology courses, professors often quotes it at about 70% genetic), but its development, refinement, and ability to be applied are subject to both exterior factors and interior factors.

Some people achieve greatness. As much as we'd all like to live a Horatio Alger story, and some people very definitely do, this is usually accomplished not merely by a belief in self, but by the extreme application of personal effort and hard work. All that hard work and effort requires self-confidence (no one would ever undertake hard tasks over long intervals if they believed they would almost certainly fail). But even though the self-confidence is mandatory to allow the hard work, the hard work is what gains the success.

And some people have greatness thrust upon them. In that sense, every major lottery winner ever has had the chance for greatness. The vast majority end up worse off in five years than before they won the lottery, again perhaps because they lacked the self-confidence or resolve to make slow, measured decisions regarding their windfall.

So while positive thinking is critical to allowing and maintaining success, it does not by itself create success.

No one can teach you to believe in yourself. Self-confidence is by nature an intrinsic value. But self-confidence is ultimately a question of perception, not of exterior acquisition of desirable traits. Self-confidence is merely the belief that you have value outside the situation at hand, and that you actually add value to the situation you are in when considering your worth.

Situations where value can be found come down to every decision or action you can take. You don't need to be an eco-nut to recycle a soda can from lunch, but you added value in making the effort to do so, and in a small way you can feel confidence about that decision. Stack up a dozen, or a couple dozen, such minor victories (whatever they constitute inside your head), and at the end of the day your mental tally will come out as success. That's all that self-confidence ever was, is or will be, the belief that the actions we undertake add value to ourselves our the situations we are a part of.

Yes, if you believe in yourself you can succeed. It's the power you have to believe in succeeding. It can be learned, but it must be taught. You have to have motivation to believe in yourself. Believing in yourself will give you the will to want to succeed and the belief that you can do it.