The Ah ha moment is one of the reasons I love tying older patterns. For example, a couple of years ago I was trying to figure out Marinaro's thorax dun. I must have tied that pattern 100 times. I read both of his books, scoured the net, talked to guys at shows, and examined flies tied by him and others. Then it just clicked. It is really cool, at least for me, because it feels like you went through the discovery process with the originator.
Guys that settle for "that will catch fish" really miss out on that sort of fun. But I guess we all tie for different reasons.
Mike.