It's weird how you can know someone for years but discover something about them you didn't know after only five minutes of talking to somebody else.

This came to my attention at work. I know many of my coworkers for years but when talking with someone I recently met at work they mentioned something about somebody that I didn't know about. like for example they know how to play an instrument. it's not something you can find out yourself but you don't know about it until somebody else mentions it and it just seems off.