Crossword puzzle clue "hard to know person"

Hard-to-know person

Hard-to-get-to-know person, so to speak

You know -- know

"Someone I know wants to know (and that someone is me)"

"I know! I know!"

Sylvia Plath poem that begins "I know the bottom, she says. I know it with my great tap root"

"Demand me nothing: what you know, you know: From this time forth I never will speak word" is his last line

Goo Goo Dolls song that you probably know from the way John Rzeznik snarls "But you don't even know who I am"