A society grows great when old men plant trees the shade of which they know they will never sit in. This proverb encourages people to make selfless contributions that will benefit others in the future. Trees provide a habitat for plants, animals, and insects, and they help to preserve the environment. They also reduce erosion caused by rainwater, and their roots soak up water slowly, minimizing the risk of dangerous landslides.

A society is not able to grow if the elderly citizens only think about their own short-term benefits. The elderly are typically well-informed and have a wealth of knowledge that they can pass on to the next generation. They are a valuable resource that should be utilized to the fullest extent.

Jean Giono's novel The Man Who Planted Trees (French title: Le Homme qui plantait des arbres) tells the story of shepherd Elzeard Bouffier. After the death of his wife, he dedicates himself to single-handedly re-foresting a desolate valley. For three decades, he labors tirelessly to transform the barren land into a lush forest. After the war, he is rewarded with official protection of the area, and his work continues. The locals are unaware of his efforts, and assume that the fast growth of the new forest is a natural phenomenon. Eventually, he passes away, knowing that his contribution has had a positive impact on the community. The tree-planting Bouffier is an example of the selfless nature of the adage "a society grows great when old men plant trees the shadow of which they will never sit in."