this mortal coil
It’s been a while since I’ve read it, but somewhere in The Chronicles of Amber, either Corwin or his son Merlin notes that he resents pain, or depression (I forget which), because it gives you tunnel vision. It constricts your horizons, erodes your ability to cope by blacking out everything but the suffering. I’ve always thought that was a pretty good description.
The ocean is clear and deep, but on the surface its storms can be fickle and frightening.