It's not just a tick
Just like your heroes in your stories the villains need to have some depth if you want an engaging story. Or if you are an actor, an engaging performance.. Without going into some depth for each of your major characters you run the risk of having characters that are forgettable and have little impact on your reader or audience. This does not necessarily mean that you write an entire biography for each character, but a character sketch or at least an outline of formative moments in their history. What was their childhood like? Did they grow up in a nuclear family? With one parent or two? Was that couple heteronormative or some other configuration? Did/do they have any siblings? What was the relationship like between the character and their family. This should probably at least a paragraph or two because family or lack thereof is very formative in our basic understanding of the world around us. We see this affect on characters in pop culture. Luke Skywalker is raised by his Au...