Why do some people seem to think they know a lot about others, and yet they have never ever met them before in real life?

Because they read a pamphlet about a guy who had a list in the 1950s.

Perception. Filling in the blanks. Intuition. Recognizing patterns.

etc.

It's purely projection. It's the way folks are with celebrities. People like to think that if they discover enough mundane and trivial facts about a person that they can gain insight to that person's psyche. Most people like to make connections to other people and often fool themselves into believing they have done so.

In other cases, it can legitimately happen. Like over the internet. If you know enough about a person's core beliefs, you can accurately assess what kind of person s/he is in real life. I don't know if I'd say this is common, but I'm sure it happens. Just as I'm sure people can fool others into believing they are something that they, in fact, are not.

They are judgmental

I do not know?

Because they are shallow and nasty !

If you are talking about people around here knowing you, it might have something to do with the fact that you've been pouring your guts out to us, possibly for years.

Just seems like some people that have never met you before in real life, they just seem to know everything about you and I mean it is like they have known you for 20 years and yet they have no clue who you really are and what you really do look like and what kind of person you are to your real gender male or female

Some people seem to think they now a lot about everything, full stop. Leave them to it, they usually won't be told any different......

Because they prejudge people and form opinions based on scant data. Sometimes these opinions are right, but they can also be quite wrong (see the contestant named Susan Boyle on the Britain's Got Talent clip on Youtube).

Assumptions based on stereotypes, race, sex, religion, physical appearance, etc.

Example. My wife says Obama has no class, is arrogant (yes I agree), no personality and everything he says uses mind control to brainwash Americans. And all she has to base it on is what she's seen on TV. I won't even comment on what she says about Michelle.

I don't know.

Is this irony??

Because some people think they know all.

good question! i couldn't answer it because i don't know why people who have met you a couple of times feel that way either!!!

As much as you may not like to admit it, there are a lot of similarities between people, and the more people you meet and know, the more you understand about people in general and can form opinions even when you haven't met someone yet. One of the things that humans are really, really good at is pattern recognition, and forming generalizations about people based on observational experience is just another example of that. It's important to realize that you may be wrong, and to keep an open mind, and to remember that sometimes people see patterns where there aren't any. But I think it's in human nature to try to size people up as soon as you have any information. I imagine it's an old survival mechanism.