The most fun "Gambit" card so far I have played. The goal is to deduce what cards this player is hogging before you see them and having enough resource for that card you are thinking of, and for it to actually be useful right now. But unlike chaos token probability-based Gambit, you can master this one by knowing your friend's deck and their natural progression and improve your chance.
For example if the scenario is already passed by for a while, I can guess that my fully-setup Mystic player may have a redundant spell asset on hand which they'd rather exchange for other cards. If someone is fighting for long time with more and more cards on hand, they probably have Asset or Event that triggers AoO and is unable to make use of while fighting while the Skill card that would be a dud for this are mostly used up in the fight. (Check discard pile to confirm) The Guardian player might be holding Dynamite Blast by now because half their deck already passed and there is none in the discard pile and they also have chronically low resource. There is higher chance to find an Ally on one's hand if they don't have Charisma and also have an Ally in play already. (Should not be too difficult to remember redundancy of allies and how many lacks the Unique star in everyone's deck.) This way you can find some quick soak and also give them a new card that is more useful for them.
Discard pile is likely the biggest source of open information so take note of how many dud cards like Skill and reactive Event like Ward of Protection are in the targeted player's discard pile and you can find more hits. You can also just stare at who loves reviving things from discard pile or take card from play area back to hand.