A Rabbinic Tale

A wise rabbi was walking along a road when he saw a man planting a tree. The rabbi asked him, "How many years will it take for this tree to bear fruit?" The man answered that it would take seventy years. The rabbi asked, "Are you so fit and strong that you expect to live that long and eat its fruit?" The man answers, "I found a fruitful world because my ancestors planted for me. So I will do the same for my children."