Rabbi Dunner cites Maimonides from “hilchot teshuva”, who describes 24 different types of people for whom the Teshuva process will not be effective. One of them is someone who is not part of a community.
Rabbi Dunner offers a classic explanation based on commentaries in Nitzavim, but adds an explanation of his own, based on the theories and research of the pioneering social psychologist, Leon Festinger.