Among the people near the Great Wall, there is a man who is good at mathematics. One day, a horse fled to the conference semifinals for no reason. Human misfortune is enough to express comfort. His father said, "How can this not be a blessing?" A few months later, the horse came back with a batch of good horses from the conference semifinals. Everyone congratulated them, but his father said, "How could it not be a disaster?" It's good to have money at home. My son loves riding a horse and accidentally fell off his horse and broke his thigh. Everyone expressed comfort for their misfortune, and his father said, "Why isn't this a blessing?" After a year, the northern conference semifinals attacked, and the strong men all drew bows and arrows to fight. Nine out of ten people who fought on the battlefield died. The man's son was saved from joining the army because of his lame leg, and both his father and son were saved.