The Hamlet Project

This is such a great way to say “You don’t know that? How can you not know that?” Because it’s not about the KNOWING – it’s the TELLING. Many a person will shame another person with the “Don’t you know that?” which always has an undercurrent of “What’s wrong with you? Why are you so stupid?”
Whereas “Cannot you tell that?” even though it essentially means the same thing could have a layer of remove. That is, you may know something but cannot say it. You know the answer but cannot tell it.