Sentence:  Particularly hard for the therapist to grasp are those <WSD>instances</WSD> in which the patient is manifesting an introject traceable to something in the therapist , some aspect of the therapist of which the latter is himself only poorly aware , and the recognition of which , as a part of himself , he finds distinctly unwelcome . 
Meaning of the word marked with <WSD> tags:  an occurrence of something