I think the importance of doing activist work is precisely because it allows you to give back and to consider yourself not as a single individual who may have achieved whatever but to be a part of an ongoing historical movement.
A film director has to get a shot, no matter what he does. We're desperate people.
Schoolchildren and older people like the idea of planting trees. For children, it's interesting that an acorn will grow into an oak, and for older people it's a legacy. And the act of planting a tree is not that difficult.