[stametseater]

> People return their shopping carts because its the right thing to do, but also there is minimal cost.

Apparently in some communities (such as Germany) it is believed that people cannot be counted on to return the shopping cart properly unless the cart holds a small value coin hostage. So the tolerated cost of selfless acts isn't some human constant, even in developed societies like Germany where people have their basic needs met.

In fact it's even more complicated than that, because specific kinds of selfless acts have different degrees of perceived importance in different cultures. In some cultures, it's considered very important to feed your guests, even if that means the host has to go hungry. In other cultures, feeding your guests isn't important or expected, even from hosts with comfortable abundance.