Trust You? What's in It for Me? - New York Times

Trust You? What's in It for Me? - New York Times: "Why does one person trust another? One reason may be that the two do good things for each other — the 'I'll scratch your back, you scratch mine' idea.

But often the reciprocity is not as direct. We trust people even though they have never done anything specifically for us. And people do good things even if they get no direct benefit.

There is a two-part explanation for this, scientists say. One is that we 'keep score' when we watch people, and if we see them acting in a cooperative way we are more likely to cooperate with them. The other is that we modify our behavior in response to being observed. If we think others are watching who may eventually cooperate with us, we are more likely to be cooperative ourselves."