There are realms of reality or — more exactly — of abstraction from reality in which the most complete detachment is the adequate cognitive approach. Everything which can be expressed in terms of quantitative measurement has this character. But it is most inadequate to apply the same approach to reality in its infinite concreteness. A self which has become a matter of calculation and management has ceased to be a self. It has become a thing. You must participate in a self in order to know what it is. But by participating you change it. In all existential knowledge both subject and object are transformed by the very act of knowing.

p. 124 - The Courage to Be (1952)