What does Camus mean when he refers to the "contradiction" in Myth?

There is one contradiction he keeps referring to. It is the contradiction in the book. He keeps mentioning it without explaining it, so I imagine he explained it earlier on and I misinterpreted it or something. What is he referring to?

Also, can you please speak in simple English and as if I haven't read any part of the book? Answers often include other things in the book I haven't fully grasped. Let's say I never heard of Myth of Sisyphus and I just heard a random guy mention the contradiction according to Camus and I'm curious about that. I'm just a regular guy with no philosophy knowledge who heard of Camus's contradiction and I'm just interested in a direct, one-line answer about what that is. Thank you.