Sometimes when you're on a small jet that's not full, the stewardess will tell everyone that they need to change seats to evenly distribute weight. Also, sometimes you'll arrive 20 minutes early on a two-hour flight because you had a tailwind. I find these things troubling. The fact that a machine screaming through the air at 500mph arrives 20% early because you had a tailwind, and that this machine would face problems if too many big guys sit up front should not be the case. It would be like getting into a time machine and asking everyone if they could stick their feet out to slow it down when you approached the year you want.