Since ancient times, "six" has often been used in expressions such as "six directions" and "six great things," which represent nature and the world, and "six virtues" and "six laws," which represent providence and law, and can be said to be a harmonious number with neither excess nor deficiency. "Gen" refers to a bundle of thread dyed a deep, rich black. By extension, it has the meanings of "profound," "deep," and "quiet." A person with skilled techniques and knowledge is called a "gennin," and "rokugen" refers to a harmonious sake made with the expert techniques of a master brewer.