I tend to use contradictions and quirks a lot in my writing because I feel it adds a little something extra to the characters. Although to tell you the truth, I don't overthink it either because it comes along quite naturally. Each character tends to have their own unique personalities that encompass some interesting contradictions.
As an example, Diego Silva is a very dapper and sophisticated character so it would surprise people to know that when attacking someone, his weapon of chose is a baseball bat. In fact, if you follow along in this particular series, you will see Diego bring out the baseball bat on at least one occasion per book. 🙄Definitely not something you would expect.
Another example would be Paige Noël-Hernandez who is considered one of the best assassins in the world - but she also likes to meditate and talk about self-help. Probably not what you would expect but it's sort of a neat contradiction.
To me, this helps make characters seem more alive, fun and interesting. And let's face it, we all have our own contradictions that make us unique. What are yours?