A grade is supposed to represent your ability and understanding of a topic, but that's only half the equation. Are exams an adequate proxy for ability and understanding of a topic? They aren't for me. When I want to understand something, I create something which requires and demonstrates that understanding - this could be a Wikipedia article, a piece of software, or a lecture. Nothing of value is demonstrated by sitting down for a few hours under extreme pressure and regurgitating my "understanding".