Stereotype

We have learned about stereotyping that it is a kind of prejudice where you form an attitute towars someone or some group before even knowing anything about the person, or generalizing it.

I was always wondering what a reason could be for why people tend to stereotype all the time.

One reason that I was given through my learning psychology is that we do not like those who are different than us, the "out group" therefore we tend to form attitutes about these certain kinds of people saying that they are all that way since we also judge them from their doings (since we do not know them) and not from their personalities.

I still do not understand, how humans are very aware of this fact that we all stereotype and that it is mostly false and ridiculous,(It is in our psychology book so it must mean that people are aware of it) yet we still tend to stereotype and do not learn from this idea.

Why is that? Is is because we are predisposed to do some, and from and evolutionary perspective this helps us survive and beware of the unknown, or is it just ignorance, that people simply enjoy stereotyping and disliking people who are not like them?