Once, there was a king, who loved justice. He looked after the subjects of his kingdom well. That was why he was highly respected by them. Quite often he used to roam around amongst his people in disguise so as to know about them.
Once, when he was roaming around, he saw an old man planting a sapling. He went to him and asked with curiosity, "Which sapling are you planting?"
"Mango," replied the man in a low tone.
The king calculated roughly how many years it would take for the sapling to grow up in a tree and bear fruits.
He then asked the old man, "Listen man! It would take many years for it to grow and bear fruits. Will you be alive till then?"
The old man glanced at the king and noticed unhappiness in his eyes because he wouldn't be alive to enjoy the fruits of the tree.
The old man replied, "Do you think what I am doing is useless because it won't benefit me? Do you think that I haven't reaped the benefits of other's efforts? I have also enjoyed the fruits of the trees planted by others. Don't you think I should do something to pay off the debt of others? I have planted this sapling to pay off other's debts."
The king was so happy to know his perspective of life.