Lejeune stated his philosophy as "The key to combat effectiveness is unity – an esprit that characterizes itself in complete, irrevocable, mutual trust. Now my infantry trusts my artillery and engineers, and my artillery and engineers know this so they will go through hell itself before they let down the infantry. My infantry believe that with such support they are invincible-and they are." Marshal Pétain praised Lejeune as "a military genius who could and did do what the other commander said couldn't be done."