we must study the customs of the Jewish People

"Chazal state that Minhag Shel Yisrael Torah Hu, “The customs of the Jewish People are Torah.” Most understand this statement as teaching that we must abide by the customs of our people, just as we must abide by the Torah. Rav Yosef Dov Soloveitchik (cited by Rav Hershel Schachter) explains that it means that we must study the customs of the Jewish People with the same rigor as we study the texts of the Torah. Rav Soloveitchik devoted much time in his Shiurim analyzing the basis of various customs because authentic customs have a basis in the Torah."  Rabbi Howard Jachter