The point of the following anecdote is to illustrate that one should not worry excessively, but should instead surrender his will to the decree of Allah without feeling the slightest degree of regret.
When I was in school I would study diligently to be first among my classmates. After handing in my examination paper, I would fall into a state of worry, fear, and anxiety. I would go home, check the answers from the book, give myself a grade, and then repeat the process all over again. It is obvious now, in retrospect, that not once did my nervousness raise my grades by a single percentage point.