The complaint of Qoheleth is not that it is unfulfilling, but that it doesn't endure. In the long run, we're all dead, as some sage once put it. The graveyard, said Charles DeGaulle, is full of indispensable leaders. I was in Mercy Hospital the other day and noticed that along the wall leading to the cafeteria are pictures of every chief of staff the hospital has had. Looks like they change just about each year.
Many organizations have such a pictorial hall of fame.
I doubt that many people remember much of anything else these people actually did, so a picture is all that remains. Not much endures, when you think about it. And maybe endurance is the wrong test. Maybe there is some other reason we work. Maybe we work not just to have some lasting effect on the world.