I had heard this old adage. I knew it. I learned it (again) the hard way. I had made my way aft and arrived at the port side winch which had my full attention. Knees were fully bent in the squat position and balancing on both feet. At the same moment that I reached out for the jib sheet the boat rolled. My hands came up with air and I tumbled over backwards feet out in front. Hard corners of the companionway hatch met the back of my scull with a wallop,
that I won’t forget…and neither will my crew — imagining various recovery scenarios and outcomes!

Hardheaded that I am, I knew I was okay. Only the scars remain.

Lesson learned: …which may derive from the days of sailing ships, when working high in the mast rigging and before the advent of modern safety harnesses; it was an essential precaution that each sailor should hold on with one hand at all times, while working with the other.

This gave rise to the idiom “one hand for yourself, one for the ship” This saying remains excellent advice.