On the first day of my discrete math class, my professor insisted we follow a rule of his:
If you don’t know, you should say “I don’t know.”
He repeated this all the time.
Saying “I don’t know” can help you avoid overconfidence, and remain open to new information and perspectives.
When nobody is willing to admit that they don’t know something, it becomes difficult to know who to trust, and what the truth really is.
See also: Illusory truth effect