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With the queen pinning h7 to the rook, Black needed quiet, developing play, and 11...Bd7 was the cleaner route to completing development. 11...Bf6 instead invited a fight on the dark squares that ended with Black having to give up the bishop on c3 a move later. The position remained EQUAL but White's pressure became persistent.

The c3-pawn was hanging and 15...Qxc3 would have collected it, keeping the game balanced with concrete material compensation for Black's earlier concession. 15...Bd7 ignored the loose pawn and let White consolidate, after which f5 and the queen on h5 turn the kingside into a serious attack. The lesson is to always scan for undefended pawns before completing development, especially when the opponent's structure has been damaged.