[Black to move]
After 9.Nc3, why is 9...Ne7 a strong move, but 9...Nf6 a mistake?
Because the d4 square is weak.
f6 is ruled out due to the chess rule of the diagonal square 1 space apart.
[Black to move]
After 9.Nc3, why is 9...Ne7 a strong move, but 9...Nf6 a mistake?