What concept did Kato Kiyomasa think should be studied every day?
Katō Kiyomasa was one of the most powerful and well-known lords of the Sengoku Era. He commanded most of Japan's major clans during the invasion of Korea (1592–1598). In a handbook he addressed to "all samurai, regardless of rank" he told his followers that a warrior's only duty in life was to "...grasp the long and the short swords and to die". He also ordered his followers to put forth great effort in studying the military classics, especially those related to loyalty and filial piety. He is best known for his quote: "If a man does not investigate into the matter of Bushido daily, it will be difficult for him to die a brave and manly death. Thus it is essential to engrave this business of the warrior into one's mind well."
Friedrich Nietzsche argued that Kant commits an agnostic tautology and does not offer a satisfactory answer as to the source of a philosophical right to such-or-other metaphysical claims; he ridicules his pride in tackling "the most difficult thing that could ever be undertaken on behalf of metaphysics." The famous "thing-in-itself" was called a product of philosophical habit, which seeks to introduce a grammatical subject: because wherever there is cognition, there must be a thing that is cognized and allegedly it must be added to ontology as a being (whereas, to Nietzsche, only the world as ever changing appearances can be assumed). Yet he attacks the idealism of Schopenhauer and Descartes with an argument similar to Kant's critique of the latter (see above).