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e f g 1 h Why it works
In the Blackmar-Diemer Gambit White sacrifices a pawn for rapid development and attack. After 5.Qxf3 the greedy 5...Qxd4?? looks like winning a second pawn — but it exposes the black queen for a chain of tactics. 6.Be3 (attacks queen with tempo) Qb4 (retreat) 7.O-O-O (queenside castle, rook on d1 aims at the black king) Bg4 (tries to pin the f3 queen) 8.Nb5! — double strike: the knight attacks the b4 queen AND threatens Nxc7+ with double check + king/rook fork. 8...Na6 (only defense of c7) 9.Qxb7! — queen grabs the pawn and attacks the a8 rook + the a6 knight simultaneously. No defense against material loss: 9...Qxb5 10.Qxa8+, 9...Rb8 10.Qxa6 — White wins in both cases.
Refutation
5...e6! — decline the second pawn. Black just closes the position and completes development with the gambit pawn extra. Alternatives: 5...Bg4 (pin) or 5...c6 (consolidate center) — anything is better than 5...Qxd4.