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

1.
不知道其中一半, 不了解全部情况
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!
你觉得我的工作很难?你根本不知道其中一半!
•
She's been through a lot, but her friends don't know the half of it.
她经历了很多,但她的朋友们根本不知道其中一半。