The rule
When you get dressed for someone else's occasion, the question is not what you feel like wearing. It is what shows respect for the people who asked you there. A host has gone to some trouble; turning up underdressed tells them you didn't think it worth much of yours.
Why it matters
Clothes are the first thing you say to a room. Dressing to the occasion tells your host the evening matters, and it lets everyone else relax, because nobody is left wondering who got it wrong.
How to do it well
- Read the invitation, and if it says nothing, ask. Hosts never mind the question.
- If you're unsure, go slightly smarter. A jacket can come off; it can't be conjured from nowhere.
- Dress to fit in rather than to be noticed. The occasion belongs to someone else.