If the object is regarded as part of the subject, or as the subject itself, subject and object collapse into one another.

If the objects gets too close to us, if we regard it as a part of us or even as ourselves, the pleasant character of the representation completely disappears, and the relation to the subject immediately becomes an unpleasant relation to us since here subject and object collapse, as it were, into one another. (Rhapsody; Philosophical Writings, p. 134)