I know so many people, especially in the software industry, with an extreme aversion to saying I don't know.
They'd talk nonsense in circles before admitting that they didn't know the answer to a question.
That mentality makes no sense to me.
If you know everything, then you don't have anything else to learn and then you're done. Whats the point?
Just say I don't know what that is!, be excited to learn something new, and lets go!