Adapted from a recent online discussion.
Is it okay to accept a new invite after committing to another?
Anonymous: Give me permission to breach etiquette! Are there ANY circumstances under which I can take back my invitation acceptance to one social event in order to attend another?
I said I would go to a co-worker's party when he announced it over a month ago, but a close friend of mine decided to have a birthday dinner on the same night. Both of them strongly want me to come. I accepted my co-worker's invitation first, but I am a more important person to my close friend. Would I be an etiquette-less jerk to attend the birthday dinner?
Carolyn: Yes. I wish I could snap my fingers and summon all the anguished letters from hosts who threw parties for 40 people, only to have 15 show up. You said you'd go, so go. If your friend feels strongly, then s/he can move the birthday dinner to another night.
To answer your actual question, yes, there are circumstances under which you can miss an event for which you RSVP'd yes: when the thing you do instead is an unpleasant alternative to what you would have been doing. That includes being sick, being snowed in or stranded somewhere, helping someone who is sick or stranded, or dealing with a family emergency, be it a death in the family or just a flooded basement, or being held over at work. You can't trade up.
Anonymous 2: Dear Anonymous: Re: Party Etiquette — I disagree with Carolyn, etiquette be damned (or not). This is your close friend, and you clearly want to go to her party over his, not because you got a "better" invitation but because she is important to you. I think there's room to switch parties if you handle it well, which means being honest with the co-worker and telling him just that.
I think the world might be a happier place if people weren't forced into doing things based on rigid social conventions.
Carolyn: If it were a hastily planned wedding or something both significant and one-time-only — say, if someone very close were unexpectedly coming through town from far away — I might agree with you. If this close friend were sick or moving away, that would count, too.
But we're having this conversation, absolutely, because of a "better" invitation. Honoring commitments isn't a matter of "rigid social conventions," it's a matter of showing respect for the fact that hosting is a laborious bit of generosity to one's guests. Even when it's done with pleasure (as it should be) it still takes a lot of effort, and it's still a slap in the face when someone says, "I know you knocked yourself out and that I said I'd come, but I'm going to pass because I like my other friend better."
If the original party has a heavy turnout and isn't table-locked, then the RSVP'er can make a polite appearance and then ditch for the dinner. But otherwise, the host has feelings that need to be treated with more care, in this case, than one's own.