One day, Honi the circle drawer was journeying on the road when he saw a man planting a carob tree; he asked him, How long will it take for this tree to bear fruit? The man replied: Seventy years.  Seventy years?! Are you certain that you will be around in another seventy years- Honi asked?!  The man replied: When I came into this world I found carob trees that were planted by my ancestors, so too do I plant these trees for my children and for the generations that follow.  Babylonian Talmud, Taanit 23a