If you're defining something, you are, by default, defying something else.
If you're defying something, you are, by nature, defining something else.
But it's easier to defy than define. Defy is the first, and easy, step. It says that's not my definition.
It's more difficult to define. That takes another moment. This is how I see it and believe it.
Define more. You still get the defiance but it's more purposeful and evolutionary rather than just bitter.