The author's point is that the true nature of practice is that you get good at whatever you repeat. This is because practice uses the brain's built-in automation mechanism. If you spend all of your time procrastinating, for example, it becomes automatic...because you have practiced it a lot, even if this was not your conscious intent. (That is my example, not the author's.)

Taking outside money, the author claims, encourages you to practice spending money. This is at odds with what the author suggests that you should practice instead: making it.