take the wind out of someone's sails idiom
(also knock the wind out of sb's sails, knock the wind out of sb)使（某人）泄气；使（某人）不坚定
to make someone feel less confident or less determined to do something, usually by saying or doing something that they are not expecting
I was all ready to tell him that the relationship was over when he greeted me with a big bunch of flowers - that took the wind out of my sails. 我已经准备好要告诉他我们分手吧，可他捧着一大束花向我迎来——这让我的心又软了下来。