The human mind has several design flaws. One of these flaws causes you to stuff novel observations into familiar definitions when they don’t really fit.
This was useful for understanding the world fifty thousand years ago. You didn’t really need to know whether a large tan cat with fangs was really a cheetah (like the one that ate Mike yesterday) or if it was actually a tiger. It doesn’t matter, the response is the same. Run away!
Today this same reflex puts the barista who stutters into the “nervous” category. In reality he might be a confident man who happens to have a speech impediment. Or you presume someone is against abortion when they tell you they voted for George Bush.
It is problematic when this reflexive categorization happens for a number of reasons. Repeatedly dehumanize a group of people with a certain label and eventually, you can dehumanize any person by attaching the label to them.
To distinguish my point, I don’t mean that you do this with purpose (though some people do). I mean your brain does it automatically as self defense. Cheetah, run. This reflex is hard to turn off.
If you aren’t nodding along by now, consider how rare it is for a human to fall neatly into one category. He doesn’t stand up for himself, so he’s a coward? But he climbs cliffs for a hobby. Your boss makes a decision knowing it will cause you anguish, so he’s an asshole — but on the weekends he cooks meals for the homeless.
In my own experience, I have had a friend who knows me as a liberal categorize my Trump posting as “trolling”. I tried to explain to him that, no, that’s not what I’m doing, but it does look like it. It also looks like someone who is inviting others to join him from a higher vantage point — but his mind was already made up. This was despite many hours spent telling him and other friends precisely what lessons they were missing out on.
My point is that you should doubt your own perceptions, especially about people.