As we point out in our "Context" section, a bunch of philosophers have gotten inspiration from Sisyphus's eternal punishment. Perhaps most famously, Albert Camus's essay "The Myth of Sisyphus" uses Sisyphus's predicament to represent the plight of all humanity, which he says is totally absurd. In Camus's mind, our continual search for meaning in life, for some sort of definitive answer that explains it all, is some ways just as pointless as Sisyphus's eternal task. Camus didn't believe in any sort of god, or that there's any such thing as concrete truth. So no matter how much any of us would like to believe that the things we do have importance on a larger scale, they just don't. Therefore, the pursuit of anything and everything is absurd.
Before you go thinking that Camus was mad depressed, though, check out this quote from the essay: "The struggle itself [...] is enough to fill a man's heart. One must imagine Sisyphus happy." So, since there's no larger purpose to everything, we've got to find a way to find satisfaction act of well... doing stuff... whatever that stuff is. We hope that Sisyphus got a chance to read Camus's essay. Chances are, this philosophy of absurd would be the only thing to keep him from going totally bonkers.