Not sure if you misunderstood my question or if I'm missing your response. My question wasn't "What is interesting about the number three?" it was "Why do you want answers handed out just for asking?" In other words, why should an NPC 'have' to answer just because he's asked? Perhaps I should have continued with "How will it affect the game?"
Seems the game might devolve into "beat up a fae for the answer". Sounds like it would get old fast.
I'm all for using numerology along with our myths and games. You can already do so without drawing hard lines of "must answer" in the ground. Just declare you've asked three times, tag it, and add it to your social roll. Gives you a benefit but not a certainty.
You could argue that same points above with the how the game says a Fae always tell the truth.
But I'm not saying you shouldn't have some underlining game mechanics for either, nor it won't get abused in some instances. I just said I found the concept interesting enough to try adding it to my own campaign. As for 'beating-up a fae for answers', that's already a possibility. Hmm.. the skill 'Intimidation' has both a social attack (getting your answer by consequences) and one called 'Threat' ( but using the mental track instead), then we got Rapport:chit/chat to trick out info without the target knowing. None of that is 'beating-up your npcs", its just the favor the RAW and setting.
And personally, I see no more players abusing the Rule of Three then I see them mega-gaming Self Compelling, Declaration, or Scholarship-Declaring Minor Details. Yet then, I'm huge Amber DRPG GM from way back and were never worried about my players abusing my npcs. In fact, most of my players now I think would agree that it was high time that they got the chance to turn the tables. And if they wish to track down Lady Midday (the newest of my fae) to badger her about some answer they think is so damned important and invoking her nature and bypassing the more social norms... then they deserve her belligerence from that point on.
In fact, you could even award them a fate dice for that.
As for the minor fae, it sucks to be weak!
Yet thinking about it some more, I would set a certain rank within the Courts for that Rule of Three to come into effect. As in, you must be of the Courts and not just a average wyld like Toots. And with a little more thought, make the Queens immune to it. But I do understand, its a house rule for everyone's game. Heck, alot of the house rules I read here I would never use myself. But then, I've always been more interested in favor then simply game mechanics, even if it leads to the same place.