"No need to be self-effacing, Ruby. I can already tell that you're deeply talented, and I've only known you for several days. You've known yourself for your whole life -- I'm sure you know as well as anyone just how talented you truly are."

That might sum it up right there, actually, the reason why Andrew didn't find cockiness off-putting. It was a principle he operated under himself: other people may understand his genius on a surface level, but having never been inside his mind, they'd never have a full glimpse at just how great he really was. He had to imagine that other people felt that way, too. Never did the idea of self-doubt cross his mind.