411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...e5/2. Nf3/2...f6/3. Nxe5/3...Qe7/4. Nf3
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4. Nf3
White retreats the knight to the safer square, where Black will play 4... Qxe4+, regaining the pawn with tempo. However, after 5. Be2, White is up in development and Black's queen is misplaced and will be kicked via 6. Nc3. Also, the pawn on f6 is permanently misplaced, and the development of the g8-knight is hindered.