My FMIL, who I generally like, has been grinding my gears lately. Both she and my mother are full supporters of the "over-invite because people won't come" and have chosen to invite everyone on the planet to our wedding. While I understand the potential hazards with this, we actually do have space for everyone, we just don't want them there. It may be close quarters if they all come. That said, I already know of enough people who won't be able to make it that I am comfortable with our numbers.
Recently her cousin (who was invited) called to say cousin's daughter (who is in her 30s and was not invited) is "so excited about the wedding". We never, ever see this person and FI told his mom to tell cousin that daughter is not invited. But then FMIL invokes the 20% rule and says that "well, people won't come- so can't we just invite her since we know others will decline?"
We had to explain it to her that if you replace every "no" with a "yes", you end up with too many people.
Didn't seem to get it. Sigh.