It is an oft-noted clinical phenomenon that the analyst's mistakes are beneficial to the analytic process. Although the analyst's mistakes, misunderstandings, and faulty functioning have been described by psychoanalysts of various theoretical persuasions, no overall theory has been advanced to account for this clinical phenomenon. To address this theoretical lacuna the central Lacanian notions of lack and desire are brought to bear. In particular, lack, or nothing, is presented as an essential working condition of the analyst, one that if understood, recognized, and tolerated can positively inform the analyst's attitude. By contrast, theoretical biases that privilege presence can obscure lack as an important contributor to the analyst's attitude. A clinical case demonstrates that both analyst and patient struggle with deep anxieties generated by lack, and that both are repeatedly tempted to solve these struggles by settling for obsessional solutions.