Have you ever been duped?
Have you been gobsmacked by a hidden trait in someone's personality?
I have been astounded by what some old coworkers/acquaintances have ended up being: (alleged) cheater, rapist, unsuccessful thief, violent alcoholic. Thankfully I haven't been personally affected, but it makes you question your ability to judge people's characters, you know?
As much as you want to believe that people present their entire personality to you, there are some bad eggs that aren't