Elon Musk's biography by Walter Isaacson revealed that he once arm-wrestled PayPal Co-founder Max Levchin over a disagreement regarding an operating system (OS). Despite being hesitant, Levchin agreed to the contest and eventually lost to Musk. Levchin later refused to let the arm-wrestling dictate the technical decision but Musk had his team rewrite Levchin's code using Microsoft's platform.