I'll tell you why. Two reasons, really. Reason one is anticipation. You wait all year, through the winter, through the muddy spring. You spend hours on the water, all in the hope that you happen to be standing in the right place at the right time. And when the hatch happens, the world seemingly changes in minutes, and every fish you thought wasn't really there comes slinking to the surface to feed. Reason two is visual stimulation. Nothing compares to watching your fly get noticed, then eaten (sometimes in a flash, others in painstakingly slow motion).