You don’t really understand an antagonist until you understand why he’s a protagonist in his own version of the world.
this…is critical knowledge
I have a habit of doing this with almost every character on every show I watch… I reframe the story as if they were the main character and watch how it changes. It’s not even just villains – with Friends, I re-imagined it from the perspective of Mona and what it must have been like to hang out with her boyfriend’s friends. If you’re writing it’s a really interesting exercise; if you want to know if your plot is solid, rewrite the piece or scene from the perspective of a supporting character to see if everybody’s actions make sense.