history: I was walking down the street and I found a 20$ bill! I was so happy I was walking down the street and I found a 20$ bill! I was so happy Did you try to find who the $20 belonged to? 
current: It was just sitting in the grass, what am I supposed to do?
next: I would feel guilty keeping money that I did not earn or that was not mine. Maybe you could give the $20 to charity?