Several years ago, a good friend came to me and excitedly pitched his latest invention - perpetual motion. He grew more and more animated as he explained how his device used magnets...

Being young, I drew a diagram showing why it would fail. With each line, I could sense him deflating, but I kept drawing. Finally, by the time I brought up Newton, I realized that I'd gone too far.

Our friendship didn't really work out too well after that and I still feel somewhat guilty...