Like you probably tend to think that physically attractive people are intelligent, and that people with big eyes are honest.
We tend to assume that someone else’s behaviour is due to their personality rather than their circumstances, and do exactly the reverse to ourselves!
There’s a saying in psychology: every good thing that ever happens to us starts with meeting a stranger. But there also are rogues out there, so making new friends can be risky. Which means you need to become skilled at making a judgement about someone new. Who to date, who to avoid and so on.
With practice you can size up a stranger within seconds. But you’ll still make mistakes, so you also need to be careful about first impressions!