While the sage, Honi was walking along a road, he saw a man planting a carob tree. Honi asked him, "How long will it take for this tree to bear fruit?"
"Seventy years," replied the man.
Honi then asked, "Are you so healthy a man that you expect to live that length of time and eat its fruit?"
The man answered, "I found a fruitful world because my ancestors planted it for me. Likewise I am planting for my children."
Babylonian Talmud, Taanit 23a, (second or third century)