Real people are walking contradictions, and characters who aren't feel flat. I once wrote a 'villain' who just loved making elaborate breakfasts for his cat. That tiny, illogical, human detail did more for his depth than pages of backstory about his tragic past. When you approach a character with empathy, you stop asking 'what would a villain do?' and start asking 'why does this person think their actions are justified, or at least necessary?' That shift is everything. It moves them from a plot device to someone who could, in some universe, exist. Their decisions start carrying emotional weight, even the terrible ones, because the reader glimpses the flawed human logic behind them. My draft is littered with notes in the margins like 'she's scared here, not angry' because my first instinct is often to write the surface emotion, not the root one.
Some of the most chilling antagonists aren't the ones who revel in evil, but those who are utterly convinced of their own righteousness. You can't write that conviction without understanding, on some level, how a person could arrive there. It doesn't mean you agree, it means you're doing the work to trace the path. The character becomes a product of their internal world, not just a puppet for external conflict. Their dialogue gets subtext, their silences become loaded, and their arc—whether redemptive or tragic—lands with a quiet thud instead of a hollow bang. I find myself worrying about characters I wrote years ago, which is probably a sign I got something right.