Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The strong man is not the one who can overpower others (in wrestling); rather, the strong man is the one who controls himself when he gets angry."
True strength is not the strength of muscles and body. The strong person is not the one who always defeats strong people. Rather, a truly strong person is the one who overpowers himself when he is in a fit of rage, because this proves that he has the strength to exercise self-control and overcome the devil.