Grades.

Grades are a problem. On the most general level, they're an explicit acknowledgment that what you're doing is insufficiently interesting or rewarding for you to do it on your own. Nobody ever gave you a grade for learning how to play, how to ride a bicycle, or how to kiss. One of the best ways to destroy love for any of these activities would be through the use of grades, and the coercion and judgment they represent. Grades are a cudgel to bludgeon the unwilling into doing what they don't want to do, an important instrument in inculcating children into a lifelong subservience to whatever authority happens to be thrust over them.

Derrick Jensen