One day in a speech, Dogen instructed,

Students of the Way, you should not cling to your own views. Even if you have some understanding, you should practice self-reflection; there must be something lacking to your understanding and there might be a more profound understanding for you. Visit various teachers far and wide and investigate the sayings of our predecessors. Yet do not cling too firmly even to the words of those of former times. Nevertheless, thinking that your views might be mistaken, even though you believe them to be true, if there is something superior you should follow it. (Shobogenzo Zuimonki, Book 4, Chapter1)