Definition
To be suddenly shocked or confused by an unexpected negative event, leaving one unable to react.
震驚莫及
When he found out he was fired, he didn't know what hit him.
當他發現自己被解雇時，他完全不知所措。
The company experienced such massive losses, they didn't know what hit them.
公司經歷了如此巨大的損失，他們完全不知所措。
She never expected this to happen, so when it did, she didn't know what hit her.
她從未預料到這件事會發生，所以當它發生時，她完全不知所措。