Are there only 19 social biases?

Which ones are most common?

FAE

Actor-observer bias?

Yes.

Because we judge the behavior of nearly everybody we meet, and always according to our own bias.

"In social psychology, the fundamental attribution error (also known as correspondence bias or attribution effect) describes the tendency to over-value dispositional or personality-based explanations for the observed behaviors of others while under-valuing situational explanations for those behaviors. The fundamental attribution error is most visible when people explain the behavior of others. It does not explain interpretations of one's own behavior—where situational factors are often taken into consideration. This discrepancy is called the actor–observer bias."

http://en.wikipedia.org/wiki/Fundamental_attribution_error

It's really hard to understand and appreciate a perspective that's different from what we know.