Based on a true story. Patton was really in love with his own image as the ultimate general, so it's hard to tell if he was just putting on a show to make his legend grow, or if he really believed he was the eternal warrior. Probably a little of both.
Given he was partly responsible for delaying by as much as a year the advancement of british troops on Berlin (making them cannon fodder all that time) makes this very much plausible. He's an unfortunate hero. Born idiot.