An oath.

“I do not aim with my hand; he who aims with his hand has forgotten the face of his father.
I aim with my eye.

I do not shoot with my hand; he who shoots with his hand has forgotten the face of his father.
I shoot with my mind.

I do not kill with my gun; he who kills with his gun has forgotten the face of his father.
I kill with my heart.”

Stephen King, The Gunslinger