Continuity
A certain amount of continuity matters to almost everyone. Think about the different forms it takes. Some people build a reputation in a field of work or study, and the knowledge or the body of work they leave behind keeps going once they are gone. For others the thread runs backward and forward through family: their ancestry, their heritage, the people who will carry their memory. A few measure it in the number of lives their generosity reached. And then there are the possessions, the house, the land, objects that quietly announce that this person was here and was bound up with these particular things.
Even a real accomplishment can feel thin once it is finished. Say you write the novel and it climbs onto the bestseller list. Then what? The question doesn't go away. Plenty of people just keep chasing the next thing, the next relationship, the next win, and whatever they did most recently never quite settles the account. There is a difference, though, between people who locate their satisfaction in reaching the goal and people who find it somewhere along the way toward it. The ones who enjoy the road, not only the arrival, tend to come away more content.
The better kind of goal is usually one you can't just grab. It sits a little out of reach, and it keeps shifting. As you gather experience and learn more, the goal itself moves, so it stays difficult in a way that holds your interest. We are here to learn, some would say. But not everyone stays in motion. As people age and start to feel that the road ahead has run short, some pull back from anything new or hard. "What's the point?" they ask.
Some hope the people coming after them will take up the work: a group leader waiting for followers to carry it on, a parent hoping a child will pick up where they left off. Others place the thread on a spiritual footing, often one built around growth of the spirit and a life beyond this one, where the soul (or the spirit, or whatever a person calls it) can still put to use what was learned and practiced here.