Or am I imagining it?
Sometimes I have completely misjudged someone but it's usually when I haven't gone with my first impression. If I liked (or didn't) someone when we first met and then changed my mind once I got to know them better it often turns out my first impression was correct.
There's a young man, early 20s, who come to my running club. He's very quiet and a much better runner than me so I can't claim to know him well at all but he comes across as very likable and a good guy. I have no experience to base this impression on, but that's how he seems.
I bumped into him in the supermarket. He was helping a very elderly lady with her shopping. They were having a lovely time, laughing a lot and he was infinitely patient with her indecisiveness and worrying. I still know nothing about him really but what a nice young man!