We do not mirror everything we see in others. Mirror neurons only fire when you watch someone get a reward or face a threat. The firing is much weaker than executing an action yourself. But if you repeatedly watch another person get a reward or face a threat, connections build. You wire yourself to get the reward or avoid the threat in the way that you’ve seen. This research is in its infancy, but it has been learned that songbirds have mirror neurons, and they learn their songs by listening to others.
