That paraphrased quote came from a Zig Ziglar program, where he himself was quoting someone else.
If your performance in life — sports, work, relationships, whatever — isn’t sufficient for you, you could do what we all do when that happens; look at what you’re doing, and even why you’re doing it, and make adjustments. That works, yes. But there may a different element to examine.
What are the beliefs that are leading to said performance?
Remember the quote above: You cannot perform in any manner which is not in line with your belief in yourself. If you want to make $20 but your view of yourself is that you make $10, you’ll be making $10. When you’re really ready to make that $20, you need to change what you see in the mirror. At that point, you give yourself and your results no choice but to line up with the belief you have set.
You can only fool yourself for so long before you either: A) Lose the mental energy to keep doing it, and revert back to your true self. Or B) Your subconscious mind finally accepts what you’ve been telling it, and that new belief is accepted as your reality.