A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 21 May 2009
The Play Mistake section of the Good Faith Rule was removed on August 2008. So now what does happen if a player announces an action, and later he discovers he can't fulfill the mandatory targets (or the restrictions or pay the costs)? It's something that happens very often in my playgroup and it can be purely non intentional (sometimes you don't read the cards closely enough).
Can the player announce another action? Or else, does he lose the turn? Is there any penalty (such as losing any further uses of the ability, or discarding the action card)?
Brook Cunningham (rules official), 21 May 2009
The Play Mistake section of the Good Faith Rule was removed on August 2008. So now what does happen if a player announces an action, and later he discovers he can't fulfill the mandatory targets (or the restrictions or pay the costs)? It's something that happens very often in my playgroup and it can be purely non intentional (sometimes you don't read the cards closely enough).
Can the player announce another action? Or else, does he lose the turn? Is there any penalty (such as losing any further uses of the ability, or discarding the action card)?
Judging play mistakes and how to handle them is a Floor Rules situation, and not a CCG Rules situation, so it's out of the scope of this forum. The CCG Rules operate in a "logic vaccuum" (if you will) wherein it's assumed that no one makes mistakes.
The section that was removed had to do with card effects that might cause a situation wherein an action was about to be announced in Good Faith, but those effects invalidate the announcement. At the time, our stop-gap solution was to rule that such an effect caused a "play mistake". We really didn't like that (again, see above; "play mistakes" are beyond the scope of the CCG Rules), so we later issued errata to fix the problem.
This is at the core of why Determination was errata'd to react AFTER announcement, and not BEFORE.