See, it is just natural that boys like cars and trucks and girls like dolls.
So you admit to thinking girls like dolls and hating trucks?
Well, it is good to admit your mistakes. Not always but yes in this case.
While it is true that most girls like dolls and most boys like trucks, there are going to be those that don't fit that stereotype. If you go around spreading that it is always true then it will make those people feel "wrong" or "broken" and that could hurt them psychologically for a long time. It's better to try being understanding instead, and most people would agree.