Cards that subtract
Hold the A♥ on a three-heart board and no opponent can hold the nut flush — every heart hand they could ever claim is one notch smaller than yours. A blocker is information you own for free: your two cards delete combos from their fan before the first chip moves. Blockers matter most in river decisions and bluff-picking — bluff with the cards that make their strongest stories impossible, value-bet with the cards that make your own unbeatable.