Why does this bother me? Details inside?

Early last week a woman came to my office door who was obviously in need. She asked if I could give her a ride. When I told her no I couldn’t, that I was the only one in the office at that time and could not get away she asked if she could borrow a few dollars for a meal and pointed to a couple of restaurants across the street.

I only had a twenty so I gave it to her and asked her to bring me back the change whenever she was through eating.

Shortly, she brought me back $10.00, thanked me and that she would return the other $10.00 later when she had the cash. I told her if she came by and no-one was in she could drop the cash in a lockbox in the door. She walked down the street and that was that.

I did (do) not expect to ever see the cash again, that was fine and if she had said thanks and walked away without indicating she would repay the money that would have been the end of it but now I find myself checking the box each day hoping to find $10.00 and each day I am disappointed.

Why?