It is wiser to say, "I don't know".
The other day, in one of my classes, I said, "A teacher who can say 'I don't know' when he or she doesn't know something is more trustworthy.
One of the students nodded his head.
Still, I agree. This is not limited to the education industry.
Human knowledge and memory are so vague that it is better to be able to say, "I don't know about that," than to say, "I don't know about what I don't know.
On the contrary, I think it is better not to say things about things we don't really know, such as, "That's what it means," or "There was a bottle lying on the ground at that time," without examining it carefully.
It is more discreditable to pretend to know something that you don't really know.
If someone loses trust in me because I "don't know," I don't think I would have had a long relationship with that person anyway.