When planning a party, I assume about 1/3 of the people I invite will RSVP and only 3/4 of them will show. I plan with that in mind. I also explicitly state the plans around food, drink, etc., and if they should come hungry or just expect snacks. And I make sure that I understand what other events or competing parties might be going on to help adjust expectations. Also, planning an annual/regular thing so that people get used to it being something they do every year helps, but it takes a couple of times to get it kickstarted.

Since I started doing that, I’ve had a lot fewer disappointing events. Event planning is a lot of work.