A teaching on the mitzvah of dwelling in the sukkah from Menahem Mendel of Kotzk, Ohel Torah, Lechag sukkot.
Rabbi Abba bar Zabda said in the name of Rav that a person in discomfort is exempt from the mitzvah of dwelling in the sukkah (1). The essence of dwelling in the sukkah is to get out of your usual, fixed dwelling place — where your thoughts usually “live,” that is, what normally occupies your mind — and to lose yourself and your thoughts in God. If you truly do this, then you won’t feel any discomfort, because you won’t feel your own self at all, for you will have no existence apart from God. “A person in discomfort,” then, is someone who has not lost himself in God and has not properly fulfilled the mitzvah of dwelling in the sukkah, therefore he has nothing to do with this mitzvah and cannot be expected to fulfill it.
1) Sukkah 25b