Blockers
Cards in your own hand that remove matching combinations from an opponent's possible range, since they cannot hold cards you already have.
Holding an ace makes AA, AKs, and suited-ace bluffs rarer in an opponent's range, simply because there are fewer aces left in the deck for them to hold. In a close bluff-catching spot, a blocker to the value hands (or to the bluffs) can swing the maths enough to turn a fold into a call, or the reverse, without changing anything about the strength of the hand itself.