Evil Is Cool, right? Wrong! Despite what certain morally ambiguous personages would lead you to believe, being evil isn't all it's cracked up to be. It can destroy your character, your soul, and everyone you love and care about. While evil may be temporarily satisfying, like cookies, the moment of sweetness can cost a lifetime of regret.
Oh, Evil Lord Bob may enjoy his reign of terror for a while, but the consequences will eventually catch up. There's always someone looking for revenge, possibly someone motivated enough to cross the Moral Event Horizon themselves in pursuit of vengeance. Even if Bob survives, he'll have to live with the knowledge that he made another monster and loosed it on the world. If Bob lets his fear and anger have free reign, he'll come to realize that the raw emotions he thought were his strength now control him. Bob might even go insane, which isn't as fun as it sounds.
If Bob is wise, he will come to understand that true happiness can only be achieved through The Power of Love or The Power of Friendship. Anybody can cross the Moral Event Horizon, but the aftermath looks pretty bleak. Nobody wants to be Bob's friend, he has nothing to show for his career in evil, and he's quite likely made the world worse instead of better, not to mention Starscreams at every corner. And through it all his soul has become so deadened that not even Evil Feels Good anymore — in fact, he doesn't even remember how to feel happy.
Compare This Is Your Brain on Evil, Guilt-Induced Nightmare, and Video Game Cruelty Punishment (in which a video game enforces this trope). Contrast Good Feels Good (which sometimes leads to this Trope, or vice-versa, if one character is able to experience both Good and Evil in his career) and Moral Pragmatist, where Bob is whatever alignment helps him reach his goals. Pity the Minion with an F in Evil and the Ineffectual Sympathetic Villain, because being evil can feel even worse if the character is bad at it.
If the same work also argues that Being Good Sucks, see Crapsack World.
The Complete Monster cannot fall under this trope, as they are good at being evil and proud of it. For these kinds of characters, being evil rocks!
Truth in Television to most people and for very good reason. We won't discuss that.
