I met someone on a plane the other day. She was off to Europe to go to school for a few months. She was on a strict budget, and asked if the airport in Canada would take US money or if she had to exchange some to buy food. I had some Canadian money with me, so I gave her a $20. She wanted to pay me back, but I told her to pay it forward. When she can afford it, she can help someone else out.
She's planning on being a teacher. So my act of kindness may have an exponential effect.