Robert and Emma are a couple living together. Robert is rich, while Emma is broke. One day, Robert places a $50 bill on the table in their living room and leaves to go to the bathroom. Emma sees the bill and takes it for herself. When Robert comes back, he doesn't see the $50 bill; he asks Emma what happened. The woman said that a gust of wind had blown into the room and the bill flew out of the window. Robert didn't believe Emma and asked her to give him the money back. Why?