On longevity and leaving a mark

There is such a beautiful idea I accidentally heard today:

A society grows great when old men plant trees under whose shade they know they’ll never sit (Joycelyn Elders, 1992).

This is a paraphrase of the Elton Trueblood’s

A man has made at least a start on discovering the meaning of human life when he plants shade trees under which he knows full well he will never sit (Elton Trueblood, 1951).

This is the degree of long-term orientation that sounds so foreign to the instant gratification reflexes nourished in the contemporary mass culture. In fact, we were born in the world were the trees were planted by someone ahead of us. Is not that wonderful that we can enjoy their beauty? Is it not wonderful to transcend one’s own existence beyond the mere birth-death time period to fill that dash with a meaning? What mark are we leaving behind and I am not talking about the trees only? What kind of legacy one is building and how long will it last?