Condition 1 - the gap card (King) is held by the LHO. The gap card is "upstream" of the tenace. Declarer assumes the gap card is held by the LHO and leads a low card toward the tenace in the dummy.
    • If the LHO plays the gap card (King), the dummy plays the higher honor (Ace) and wins the trick. The dummy's lower honor (Queen) is now the highest card in that suit. The dummy leads the lower honor (Queen) and likely takes trick. The finess worked.
    • If the LHO does not play the gap card (King), the dummy plays the lower honor (Queen) and wins the trick. The dummy leads the higher honor (Ace) and wins the trick. The finess worked.
        • If the King was not played, it was because its was "protected" by two other lower cards. You were going to loose it anyway. At least both of the tenaced cards took a trick.

Condition 2 - the gap card (King) is held by the RHO. The gap card is "downstream" of the tenace. Declarer assumes the gap card is held by the LHO and leads a low card toward the tenace in the dummy.
    • The LHO does not play the gap card (King), so the dummy plays the lower honor (Queen). The RHO plays the gap card (King) and takes the trick. The finess did not work.