That just doesn't seem that different than the player deciding there are spellbooks. It just makes you roll to see if the player is right. The rules are supporting the idea that the player can generate fiction that the PC is not directly responsible for in the fiction.
What do you mean by "generate"?
The player puts a possibility on the table - there are spellbooks. The player does that by authoring nothing beyond their PC's action - "I search for spellbooks". (Vincent Baker calls this
making a suggestion about the content of the shared fiction:
lumpley games: Roleplaying Theory, Hardcore)
There are some RPG systems where the player, having made such a suggestion is able to deem it to be true in the fiction. An example is Marvel Heroic RP: under certain conditions, for instance, if you are playing Dr Strange or Dr Fate or a similar magic-using superhero, then you can spend a "plot point" to make it true in the fiction that you have found some useful spellbooks. (The technical label the game gives to this is creating a
resource.)
I did not describe such a game in my post. The player has put a possibility on the table. The next step is to work out
whether or not that possibility is true within the fiction. How do we work that out? The player doesn't get to spend a point to author it. The player doesn't even get to roll a die to author it. The action resolution rules are invoked, and these are "say 'yes' or roll the dice", with a rule about what happens on a success (the player's declared intent and task become true within the fiction) and a rule about what happens on a failure (the GM narrates an adverse consequence, paying particular regard to making sure the player's intent is thwarted within the fiction).
The mechanical process is one that the participants have all agreed to, in agreeing to play BW. (It's rules on this are super-clear.) And the mechanical process is one that takes the power
out of the hands of an participant, and puts it with the dice.
I mean, suppose that you and I are deciding which movie to see. I suggest one, you suggest another. We agree to toss a coin: my movie on heads, your movie on tails. If the coin comes up tails, we're seeing your movie. But you didn't choose which movie we're seeing! We resolved that via a coin toss. The whole point of having the coin toss was to relieve both of us from the burden of decision.
EDIT: This might also help make clear the significance of "nothing happens" not being a move. (BW doesn't use the terminology of "moves", but it has a similar idea to the principle that I've stated upthread in relation to AW and DW.)
If "nothing happens" was a permissible GM narration on a failure, that might produce degenerate gameplay, because a player would not have to stake anything, or take any risk with their PC, in declaring actions like "I look for spellbooks". But every action declaration is either just "waved through" - the GM says "yes" and play goes on, somewhat similar to the idea of a "soft move" in AW/DW - or else a roll is called for, resolved as per what I've described in this post and upthread.
No action resolution leaves the situation the same coming out as it was coming in.
