のに details
write + even though
kaku noni
even though; despite; and yet
約束したのに、彼は来なかった。
yakusoku shita noni, kare wa konakatta.
Even though he promised, he didn't come. neutral
言ってくれれば手伝ったのに。
itte kurereba tetsudatta noni.
If you'd told me, I would have helped. casual
Examples
even though — a fact whose natural consequence failed to follow, tinged with surprise or complaint
約束したのに、彼は来なかった。
yakusoku shita noni, kare wa konakatta.
Even though he promised, he didn't come. neutral
あんなに練習したのに、負けちゃったよ。
annani renshuu shita noni, makechatta yo.
After all that practice, we still lost. casual
何度もご説明したのに、ご理解いただけませんでした。
nando mo go setsumei shita noni, go rikai itadakemasen deshita.
Despite explaining repeatedly, I could not get them to understand. formal
sentence-final のに — the expectation trails off unmet, voicing regret or reproach
言ってくれれば手伝ったのに。
itte kurereba tetsudatta noni.
If you'd told me, I would have helped. casual
せっかく作ったのに…。
sekkaku tsukutta noni...
And after I went to the trouble of making it... casual
Formation
{V}のにattaches to dictionary formplain clause + のにattaches to plain clausei-adj + のに (高いのに)attaches to i-adjectivena-adj + なのにattaches to na-adjective{N}なのにattaches to noun
Notes
Related patterns
Similar
ても can concede a mere supposition (雨が降っても行く plans around rain); のに cannot — it protests a realized fact whose expected consequence failed (雨なのに行く — it is actually raining).
Both link contrasting clauses, but けど merely juxtaposes (高いけど買う notes the price), while のに protests a violated expectation and often reads as complaint (高いのに買う implies the purchase defies sense) — swapping のに in for plain けど adds reproach the speaker may not intend.
Lookalikes
One kana apart on the identical attachment (雨なので／雨なのに) — ので gives the reason for what follows, のに protests that what follows defied it; dropping the wrong final syllable silently flips the sentence's logic.