Politeness and Indirectness: `有事` is a cornerstone of indirect communication in Chinese culture. Saying `我今天有事 (Wǒ jīntiān yǒushì)` — “I have something on today” — is a perfectly polite and complete way to decline an invitation. It avoids the need to provide a specific, potentially awkward excuse. This protects the “face” (`
面子`, miànzi) of both parties; the person inviting isn't directly rejected, and the person declining doesn't have to lie or overshare.