Believing in yourself is self-efficacy. Believing in yourself is confidence in your own ability, knowing what you have to do to win or simply to get what you want in life.
In addition, you may also be comparing yourself with others. Remember, nobody is perfect. Others may also have their failures that you are unaware of. You see only their successes but not their failures. Surprisingly, seeing your own imperfections may be the pathway to future success.