のに

のに is used to express a contrast between two situations: what actually happened or what is true, and what was expected or desired. The first clause states a situation, and のに marks that the second clause contradicts that expectation, often with a sense of disappointment or irritation. It is common in everyday conversation and can carry a mild emotional nuance (frustration, surprise). Note that the first clause is in the plain form (non-polite). In a more formal setting you might replace with a different contrastive structure, but のに itself remains informal or neutral. Keep in mind that the second clause usually expresses an outcome that is undesirable or opposite to what the speaker expected.