Tommy MacWilliam:

Not only do smart people ask questions when they don’t understand something, but they also ask questions when the world thinks it understands something. Smart people challenge the very limit of human understanding, and push the envelope of what’s possible farther than many people would argue it’s meant to be pushed. Smart people don’t take claims at face value, and smart people don’t rest until they find an explanation they’re comfortable accepting and understanding.

Smart people are comfortable with the idea that they still have something to learn.