I can agree that bad grades, or bad days, are not necessary.

You don't need to have something be bad to know when you experience the best.

Why/How? While there are certain types of "good" or "best" days that can be earned, some are just super simple. One of my best days was when I was a kid on family vacation to the beach. Sure my parents worked to earn that. I was just born into a family lucky enough to go to the beach that one weekend.

..... best is best. You don't have to have an F in a class assignment to know your best grade on an assignment was the 100. It doesn't matter if all your other grades were 99. The 100 is still your best and will feel damn good.