The Question Why does sleep matter? Every animal with a brain sleeps, even at the cost of vulnerability to predators. Evolution rarely preserves something so costly without a serious reason. The reason, we now believe, is memory — not just storing it, but reorganising it. Sleep is when the brain edits its own recordings. This raises a question that nobody had seriously asked until recently: what happens when you give an artificial neural network something like sleep? And what does the answer tell us about why current AI systems, despite their impressive capabilities, cannot think genuinely novel thoughts?