There is an insane amount of psychology involved in a USN's submarine watch rotation. A large part of it is designed to keep people busy (or sleeping) so they're not thinking about how much the world wants them dead for thinking it's a good idea to float around crushing pressure of the depths in what is basically a giant sardine can.

(and lets be honest, we all have a vested interest in them not going insane from huffing their own farts.)