Breakthrough
Those moments when I finally solve a problem that I've been beating my head against for a while, only to discover the solution is rather simple, are quite bittersweet. I feel awesome and triumphant, because I've found my answer and I don't need to worry about it anymore, but I also feel like an idiot for not taking so long to come up a now-obvious solution. But I suppose, anything is obvious once you've found it.