If you read a biography of O'Sensei you will find he had a fanatical desire to be stronger than anyone else.
"The Founder was full of youthful vigor. He had an unyielding spirit. If others did twice as much as ordinary people, he would do four times. If others carried 80 pounds, he would carry 160 pounds. His quick temper found good opportunities for expression in the rice-cake-making contests of his village.
In these contests a large scoop of a special type of cooked rice is placed in a huge stone mortar or bowl. Then a large sledge, something like a wooden mallet with elongated head, is used to pound the cooked rice. An assistant constantly turns the rice over on itself as it is being pounded. Gradually the rice is transformed into a rubber-like substance which is laid out in flat cakes to cool before eating. The weight of the sledge with its awkwardly-shaped elongated head, and the force and frequency of the kneading means that making the cake required.
In these contests the Founder eagerly matched himself against other strong young men-four, six. Then ten. All were defeated. Finally the Founder broke the pounder. He would go to other places to pound rice and again broke many pounders. People eventually had to politely refuse the Founder's offer to help make rice cakes for fear he might break more of them. Instead, they served tea and pastries, in the Japanese way reserved for honored guests, to keep him away from the rice-cake-making area."