not know the half of it idiom informal (also have not heard the half of it)
不知道更严重的情况
If someone does not know the half of it, they know that a situation is bad but do not know how serious it is.
"I hear things aren't going too well at work." "You don't know the half of it!" “我听说工作进展得不太顺利。”“你还不知道更糟的事呢！”