Musashi had always been a bit unorthodox and hard to predict, but he took the stakes up for this duel. The time of the engagement came, and Musashi didn’t show up, forcing Kojirō to wait for hours by himself. This induced “uncertainty” in Kojirō. With the benefit of psychological research, we now know that any time there is uncertainty in a person’s future, they begin to drain cognitive resources trying to “predict” a moving target. Musashi didn’t know this scientifically, but he understood it intuitively.
By the time Musashi showed up, his opponent was already a bit mentally drained because of this. But Musashi also showed up with the wrong weapon… he was known for fighting with duel katanas, a fighting style that Kojirō had likely studied in preparation for this duel. But Musashi arrived with his own long-blade that was longer than Kojirō’s blade. This meant that whatever preparation Kojirō had done to prepare for the duel was now irrelevant.
Despite all of this mental manipulation, Musashi came the closest he’d ever come to death by duel during his fight with Kojirō. He won, in the end, but it was too close for comfort. This dance with death created a rip in Musashi. After the duel, he disappeared into the mountains and no one heard from him for several years.