Relaxing in a physical conflict is counter-intuitive to most people's thinking, because when someone grabs you or tries to strike you, you tense up.
We were working on katate-tori tenshin-nage irimi, exploring how to take uke's balance and move smoothly through the throw without having to muscle it. Focusing on the four basic principles.
One of the new students gets told, "Relax".
He replies, "It's hard to force yourself to relax."
He's right, of course, you have to relax and let yourself relax.
His reply is pure Zen, though, just an honest observation of his experience at that moment.