平白无故

平白无故

Literally means:

without any cause or reason

Actually means:

for no reason at all

平白 means for no reason; 故 means reaso reason.

This phrase means for no reason at all. It is often used to describe something groundless or something that happened without any obvious reason.

平白，凭空；故，缘故。

没有原因、没有理由。多用来指看不出某件事情的发生有什么理由或根据。