Luffy had no time to be overconfident in his abilities, having spent his childhood in defeat at the hands of Ace, Sapo, and even the Haki user Garp. Through his experience in numerous actual battles, he is well aware of his vulnerability to slashing attacks and even the risk of having his outstretched arm cut off. In a battle with Kuro, who boasts of his high speed, Luffy experienced being ridden by an unprotected outstretched arm, and during the Summit War, he successfully avoided the danger of having his arm amputated by Mihawk.