Why are humans so smart about what other people do?

Mirror Neurons - Cells That Read Minds - New York Times

We humans have neural nets that fire our feelings and perceptions when watching others.

The human brain has multiple mirror neuron systems that specialize in carrying out and understanding not just the actions of others but their intentions, the social meaning of their behavior and their emotions.

Of course, I can be dumb about people..

Added - I changed the previous odd tense of the headline and added a bit more detail.