I can't now find the reference but what passes for my memory tells me that the research into how people reach conclusions about each other indicates that most people have reached their first conclusion, about someone they've only just met, in as little as five seconds. I can't recall exactly what the research indicated about the accuracy of such judgement but it seemed to be supported more often than not.

Fortunately, most of us are good learners.

Cheers, Rowan