This is basically story which I love. I read this when I was a kid in school but I still remember it clearly because it taught something in a very subtle manner. Here is how it went..

One day Joey saw his grandfather planting a mango plant sampling into the soil. He went across to his grandfather, who was very old, and asked him the reason for planting a mango sampling when it would not be possible for him to see the it grow into a tree and bear fruits. The grandfather smiler and replied that when he was Joey’s age he had eaten several mango fruits by stealing them from the neighborhood gardens and had enjoyed the taste of it, now was his turn to plant a sampling which would grow into a tree someday when he was not alive and whose fruits would be enjoyed by kids just the way he had done. This way his debts would be fulfilled.

End of story. The lesson being that the society we live in provides for us when we are growing up, it becomes our responsibility to return back something to the society as a way of clearing our debts. If you are going to pollute the environment around you all the cars & buses we are using it important to neutralize it by planting trees and garden plants as much as possible. This way the balance cant be maintained and we can contain the pollution.