Question on questions?

I have read a lot of questions here on answers, but have chosen not to answer them all.

What I have seen I is a lot of stereo-typing.

We all do it in one way or another.

such as

1.I will never eat at McKings again

because I had a bad expierence at the one up the street.

2. I wll never drive a Foryota again because the one I had before kept breaking down.

Those are the safe stereo types.

Now for my question

Why is it when you or (anyone) sees one goupe of people either on tv or in their personal life do something bad they tend to believe everyone of that gender or race is the same?