by surprise
Unexpected, Chinese idiom, Pinyin is ch ū Q í B ù y ú, meaning unexpected, refers to unexpected action. From Duan yongzhuan, the book of Zhou.
source
Duan yongzhuan in the book of Zhou: "if the stars are flying fast, you will be able to ride five hundred skillfully and be self-sufficient."
usage
As predicate, attributive, adverbial; with "surprise".
by surprise
be struck by lightning and split into two halves - tiān dǎ léi pī
one falling leaf is indicative of the coming of autumn - yè luò zhī qiū
mind one 's own business in order to keep out of trouble - jié shēn zì ài