Why not defending with the queen?

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shmiro27

Hello! I have recently started studying and playing chess. Currently about 1200 on chess.com.

I have reviewed a recent game and not sure about this spot: (I play black)


I played Qd6 because I thought it defends the knight on e5 but still maintains the double defence on the pawn on d5 as well.

The engine however considers this move as a mistake and suggests that Nc6 is best.

Why is my move bad and the Nc6 so much better?