The faulty belief that we are incomplete, inadequate, less than or empty. We blame our supposed lack on what the world has done to us and try to fill it by gaining the world's idols (see T-29.VII.4) and its acknowledgement of our specialness. Yet lack is caused by our own belief in separation, which causes us to feel lonely and cut off. Lack is solved by realizing that we are not separate and are already complete. See having/being. See T-21.I.1:6.