On a form somewhere you've written it down. Name. Nationality. Religion. Occupation. Marital status. Race. The form imagined you could fill in those blanks. You imagined it too. You wrote American. You wrote married. You wrote engineer. Each answer felt like you describing yourself.
K's question is who made those answers. You didn't choose to be born inside a border someone else drew. You didn't choose to be Christian or Jewish or Muslim. Your parents whispered prayers over your crib in whichever language was nearest. You didn't choose your first language. You didn't choose what food felt like home. You didn't choose which faces felt like family and which felt like strangers. By the time you could choose anything, the choosing had already been done.
This is K's first move against the self. The "I" that says "I am" didn't author its own contents. It's a recipient, not a creator. It received an inheritance and then started calling the inheritance "me."
Most people respond to this with defensiveness. I chose my politics. I worked for my degree. I built this life. All true. And all built on a self that didn't choose to exist with those predispositions, those tastes, that language, those formative figures. The choices you made were the choices the inherited self was capable of making. The self was already loaded when it started picking.
The self is downstream of decisions the self had no part in. Defending it is defending someone else's work, mistaken for your own.