Camus uses the Greek myth of Sisyphus to really nail this point home.
Sisyphus is one badass guy and he's running around, being an asshole to the gods. He chains up death and then spills some beans about super secret god stuff.
So they grab Sisyphus, give him a boulder and tell him to roll it up a hill, but, when he rolls it to the top, it rolls back down. In fact, every time he rolls it up, it rolls back down. He is performing a task of absolute futility and meaninglessness.
Sisyphus is in a good position — he knows that his purpose, his actions in life are meaningless and he's stuck there, he knows this too, because he is condemned.
But Sisyphus, at least in Camus' interpretation, is one smart guy. Sisyphus doesn't hope that things eventually get better. He doesn't develop some deity or pray at the gods to stop his suffering. He doesn't jump off the top of the mountain to end his suffering and kill himself.
No...
Sisyphus enjoys it.
He is in the moment. He embraces the absurdity of his condition and, by enjoying it, he revolts against it. He is scornful.
Each atom of that stone, each mineral flake of that night filled mountain, in itself, forms a world. The struggle itself toward the heights is enough to fill a man's heart.
"One must imagine Sisyphus happy." -Albert Camus
