I really like this!!! I might make one tiny tweak to it and say:

Instead, think of the antagonist as something/someone that is everything your protagonist doesn't want to be.

By definition, the antagonist in a story is the person causing conflict for the protagonist, right? Which, as MontyB said, is not always the "villain" (if there is one.) Sometimes it's even the protagonist himself, stepping on his own toes by doing stupid things. Let's say a main character blows off study to go to a party, fails the test, fails the class, fails out of school, and ends up living on the streets, addicted to drugs, in jail, or some combination of those. In that story, the main character serves as the "ultimate warning sign" to himself - when he's faced with the decision and makes the wrong choice, it defines the whole path of his life. He knew better than to blow off study time. In his heart, he knew it was the wrong choice. If it caused him to fail out of school, surely he knew what a dire situation he was in. He didn't want to be that person, the guy who fails out of school. But he wanted to go to the party so badly that he justified the decision in his own mind, probably by telling himself this one decision, this one test, didn't matter. He could make it up some other way. Except, he couldn't, and he because the person he didn't want to be.

Cheers,
Michelle