What things can cause a person to be baised

What can cause a person to be biased is by what they think.

For instance, I like chocolate cake, someone out there doesn't like chocolate cake; but I am biased and saying that chocolate cake it the best and you will like it because I like it.

That is biased.

So what people think and view a certain thing causes them to be biased.

religious views, political views, and upbringing