The Myth of Sisyphus
This is Camus working out on paper what The Stranger only shows you, and the two came out the same year. It opens by declaring that there is one genuinely serious philosophical problem, suicide, because everything else is secondary to whether life is worth living. He then refuses both of the available exits; actually killing yourself, and what he calls philosophical suicide, the leap of faith he accuses Kierkegaard and a few others of taking. What’s left is carrying on with no appeal to any larger meaning, which he insists is not resignation but revolt. Then the rock, the hill, the eternal business of pushing it up and watching it roll back down. Everybody quotes the last line, but the bit that does the work is just before it; the descent is where Sisyphus is conscious, and that hour is the whole point.
A much harder read than the story version and not for the faint of heart. However, it’s one I’d always recommend re-reading.