Self-esteem is extremely important and a matter of discussion. If you have high self-esteem, you are more prone to believe in your possibilities of achieving your goals. You feel precious of the rewards that accomplishing your goals will carry e.g. a higher income. This better confidence and feelings of value lead you to work harder in chase of your goals. A bit like a self satisfying prediction, believing you can attain your goals, and working harder to get them, greatly boosts your chances of success.
People having low self-esteem, the contrary is true. You do not consider in your ability to realize success and you feel worthless of the rewards which that achievement would bring. Therefore you do not work as hard to meet your goals and you consequently fail to attain them.