Sometimes, the monster that is scariest is 

 the one you can’t see. The one you cannot see, 

but you know is there. It’s waiting for you in

  the depths far below, watching your two limbs flee. 

That’s why sailors, by far, have the most courage.

 There is always the chance the ground disappears.

And if, God forbid, it did, who would notice? 

 No one is watching except the distant pier.

Life requires many leaps into unknown.

 You become the sailor on the blue monster.

 The ground is gone and you find yourself alone

  No land in sight, for miles–only water.

  Frightening, but you have to swim to safety;

There’s no monster but yourself in the deep sea.