During and after a relationship (friendships, in my case) I tend to analyse their behaviour and our dynamic, which then develops into a "sense" where I feel as though a person is similar to a Key Person (who was in my life/had a big impact on me). 

E.g: I had a friend who had similar opinions as me, but would dominate the conversation and constantly vent though nothing I said helped them. So now when I get the sense that someone is like that friend, I avoid them. 

Maybe I'm just learning from my mistakes but I get the feeling I may accidentally create high standards for people, and that I'm categorising them unnecessarily. There's also a chance I'm not treating the person as themselves, but treating them like a Key Person just because they remind me of them and having emotional flashbacks with every person I meet.