Hello I am a beginner stuck at 650 trying to improve Could someone explain why this is a miss?

https://www.chess.com/analysis/game/live/122352571589?tab=analysis&move=16

On move 9, I missed the only move in a critical situation. I don't really understand why, can someone explain this to me please?

Also sorry if this is the wrong place to post for help, I wasn't sure. 

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Hey there.

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In the diagram you will see a more in depth reason, but in short, Nd4 is much better than anything else, so everything else is inaccurate.

Nd4 was the move, you just win the c6 pawn since your knight attacks it and now that you moved the knight the bishop also attacks the pawn. If he pushes the pawn up then your knight can take his bishop on e6. When he takes back the knight you have the move Qa4+, attacking the king and the knight which is a fork. His rook is also exposed to your bishop now, which you may be able to take on a subsequent move. Black's best response is to castle and when you take the pawn on c6, you are up a pawn with a good position and the advantage. Hope this helps! Engine considers your move 9. Nd2 a miss because 9. Nd4! is the only move to take advantage of black's mistake, and your move 9. Nd2 is just equal.

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