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, 15 May 2014
I'm fairly sure that this is cut-and-dry, but I just wanted to check.
Is there a difference between 'Invest 0G' and choosing not to trigger an invest trait with a cost of 0G? I assume that this is correct as otherwise a player may be forced to make decisions they didn't intend based on an invest effect they didn't want.
For a practical example:
I announce Inspired Leadership. When paying costs I state 'Invest 0 gold', I must target a tactician, whereas if I do not state 'Invest 0 gold' I am free to target non-tacticians, even though in both cases 0G has been spent, correct?
I assume that you cannot announce 'Invest 0 gold' if you have no tacticians to target (ignoring the chance of any future cards that may give tactician as in interrupt: I assume that such a card would have to exist before the game worries about its potential to affect the game state).
A player, 2 June 2014
The CR paragraph referring to targeting paradoxes has been updated. See pp. 33-34
Choice paradoxes : If a choice (such as choosing a target, cost payment or announcing an Interrupt) requires information from another choice that has not been made yet, the player must make that second choice at the time of targeting or payment, as a prerequisite for the first choice. He or she must also stay with that choice through the rest of the action or trait in question, until the choice is officially called for. In such a situation, if the game state changes so that the choice is no longer valid, then the player cannot make an alternate choice; the cost is not paid, or the effect fails, as appropriate.
You cannot legally announce you're paying an Invest of 0 for Inspired Leadership, and later make another choice that doesn't fulfil the condition for the reduced Invest cost. If you choose to pay "Invest 0" at the cost payment step, you must stay true and target a Tactician.
Of course, if you don't announce that you're activating Invest, you're free to target any legal non-Tactician