He remembered the old-timers from his navy days. Grizzled lifers who could soundly sleep while two meters away their shipmates played a raucous game of poker or watched the vids with the volume all the way up. Back then he'd assumed it was just learned behavior, the body adapting so it could get enough rest in an environment that never really had downtime. Now he wondered if those vets found the constant noise preferable. A way to keep their lost shipmates away. They probably went home after their twenty and never slept again.