just the opposite to what one wishes
at cross purpose
at cross purposes
opposite of one's wish.
例句
其結果必然不會像他們所壹廂情願的那樣， 而只能適得其反。
The result will definitely turn out to be just the opposite of their wish.
事實上，那樣做的效果可能適得其反。
In fact, it might have just the opposite effect.
然而適得其反，曾芮竟然以死相逼，家裏陷入混亂。
Counterproductive, however, had forcibly imposed Rui even death, the family into chaos.
然仍，知道目前，奧巴馬令人惋惜的推銷術適得其反。
So far, though, Mr Obama's lamentable salesmanship has pushed harder the other way.