not know the half of it
US /nɑt noʊ ðə hæf əv ɪt/
UK /nɑt noʊ ðə hæf əv ɪt/

1.
절반도 모르다, 전부 모르다
to not know the full extent or all the details of a situation, especially one that is more serious or complicated than it appears
:
•
You think my job is tough? You don't know the half of it!
내 일이 힘들다고 생각해? 넌 그 절반도 몰라!
•
She's been through a lot, but her friends don't know the half of it.
그녀는 많은 일을 겪었지만, 친구들은 그 절반도 몰라.