Fundamentally, all jujutsu could be described as the art of compromise. No, I don’t mean two people coming together and each adjusting themselves to come to agreement. And I’m not talking about “giving in to get your way,” as the book goes. In jujutsu, you attempt to compromise your opponent as much as possible, while minimizing the risk of being compromised yourself. What that compromise looks like, how it’s achieved, and how that compromise is used to conclude a combative encounter varies by art and artist, but compromising your opponent is the thread that runs through all grappling arts.
When Jigoro Kano brought together what he’d learned in Tenjin Shinyo ryu and Kito ryu, he did so around a new model for how throws work, a fundamental principle that allowed him to defeat his own teacher repeatedly. Kano’s realization was that it was always easier to throw an opponent who was already compromised. This rather obvious sounding principle certainly existed in the techniques of older arts, but it was Kano who gave it a name, much like a scientist documenting a long observed natural phenomenon. Kuzushi was born (or at least named).
Often translated into English as “balance breaking” a more literal translation of kuzushi is, “to level, pull down, destroy or demolish”. So kuzushi could be thought of as something which compromises the martial ability of an opponent. This compromise can come in many forms and can be achieved by various methods, but must significantly affect an opponent’s freedom of motion and balance. To a trained observer, this is a clearly visible state, often resulting in a near inability to move or an inability to prevent movement.