If you believe in yourself, that is certainly no guarantee that you will achieve success. You may still need to develop your skills, you may need more education, or you may need more experience. But it is guaranteed that you will not be successful if you do not believe in yourself.
If you don’t believe you can, you’re right. One of the first and most important factors in the principle of belief is that people always tend to believe that which is easiest to believe. It’s emotionally easier to believe that the perfect mate exists out there somewhere than to work on the marriage you are in now. It is easier to believe that the reason your business is failing is because the economy is bad or because you got a bad break. It is easier to believe life has been unfair than to take responsibility and admit fault.
People who are successful employ the Power of Mind and the Power of Choice to discern the truth about their situation without regard to emotion.