Lesson
White to move. Main line: 1. f3 e5 2. g4 Qh4#
After 1.f3? e5 2.g4?? the diagonal from h4 to e1 is wide open, and 2...Qh4# is mate: the king is trapped behind its own pieces on d1, e2, f1 and f2, with the g3/f2 escape controlled by the queen.
Fool’s mate can only happen to White (and only through two terrible pawn moves), but the lesson is universal: moving the f- and g-pawns early exposes the king along the most dangerous diagonal on the board.
The fastest possible checkmate
Two moves is the theoretical minimum for checkmate in chess, and this is it: White plays f3 and g4, and the queen arrives on h4 along the diagonal those two pawn moves just opened.
It effectively never happens between players who have played more than a handful of games. It is included because the mechanism is worth seeing exactly once.
Why those two pawn moves are fatal
The e1–h4 diagonal is the king’s most vulnerable line at the start, and f3 and g4 are precisely the two moves that clear it and cannot cover it afterwards. Stockfish rates 1.f3 at about −0.75 — bad on move one, before anything dramatic has happened — and 2.g4 as mate next move.
Compare f4, which also moves the f-pawn but keeps a defender available. It is the combination that kills, not the f-pawn on its own.
1.f3: About −0.75. The engine’s preferred first moves sit around +0.3, so this loses roughly a pawn of evaluation immediately.
2.g4: Mate in one for Black. Any reasonable second move keeps White merely slightly worse.
Pawn moves in front of the king are permanent — they cannot be taken back.
The e1–h4 and e8–h5 diagonals are the fastest routes to an uncastled king.
The shortest mate in chess is two moves, and it requires cooperation to achieve.
Source: Fool’s mate — https://en.wikipedia.org/wiki/Fool%27s_mate