The Guardian's answer to Ward of Protection. While this doesn't cancel the effect of the card drawn by the playing investigator, the ability to block the next copy can be very valuable, especially for treacheries that stack and build up or draw out a scenario enemy (such as Daemonic Piping) or generally annoying treacheries like Ancient Evils. In a 3 or 4 player group where you are cycling through the encounter deck fairly quickly, this is a strong addition for those who can take, and all for only 1 XP!
Fast. Play when you would discard a treachery card after resolving any of its effects.
Put "Fool me once..." into play in your play area and attach that treachery to it.
When any investigator draws a copy of the attached treachery card, discard "Fool me once...": Cancel that card's revelation effect.