The gap concept states you need a stronger hand to call than to raise.
Explanation. Introduced in 1980s strategic theory, the “gap” refers to needing a stronger hand to limp or call a raise than you would to open‑raise. The logic: calling already shows weakness and allows other players to act. For instance, you might open with A‑Q from early position, but you need stronger than K‑J to call someone else’s raise from late position. The concept underscores why position and aggression matter.