Wisdom of fingernails.

That's what Jeff Bridges said about The Dude. He oughta know.

For me, the Dude has a certain type of wisdom. I like to call it the "Wisdom of Fingernails": the wisdom that gives you the ability to make your hair and fingernails grow, your heart beat, your bowels move. These are things that we know how to do, but we don't necessarily know how we know how to do them, yet still we do them very well.

You can put that next to l'esprit de l'escalier in the Guideposts to Life file cabinet. I'm not sure there's a connection there, but I already typed it, I can't take it back now.