〜のに
even though, and yet (frustration)
Plain form + のに · Noun / な-adj + なのに
Sign up free to review this point on a spaced schedule.
のに means "even though" or "and yet", with feeling: 薬を飲んだのに、熱が下がらない, "I took the medicine, and my fever still won't go down".
It's the shape of ので, but the result goes against what you'd expect, and the speaker is usually surprised, disappointed or annoyed. けど is a neutral "but"; のに complains.
Nouns and な-adjectives take な: 日曜日なのに, "even though it's Sunday".
Said at the end of a sentence, it's pure regret: 言ってくれればよかったのに, "you could have told me". And don't mix it up with のに meaning "for (doing)", which comes a few points on.
Examples
薬を飲んだのに、まだ熱が下がりません。
I took the medicine, but my fever still hasn't gone down.
約束したのに、彼は来なかった。
He promised, and yet he didn't come.
日曜日なのに、仕事に行かなければならない。
It's Sunday, and I still have to go to work.
一生懸命勉強したのに、試験に落ちた。
I studied so hard, and I still failed the exam.
高かったのに、全然おいしくなかった。
It was expensive, and it wasn't even good.