In protecting the King's Pawn with your K. Bishop's Pawn, you are guilty
of a very common error among young players; as you improve, you will
find that it is rarely good play to move the K. Bishop's Pawn to the
third square--in the present instance, for example, you have deprived
yourself of the power of castling, at least for some time, since the
adverse Queen now commands the very square upon which your King, in
castling on his own side, has to move. Black's last move is much more
sensible. He again attacks your Bishop, and by the same move brings his
Q's Knight into co-operation with the King's, on the weak point of your
position:--

10. Pawn to Q. Kt's 3d. 10. Q. takes Queen's Rook.

This is a serious blunder indeed. In your anxiety to save the threatened
Bishop, which you feared to withdraw to Q. Kt's 3d sq., on account of
the adverse Knight's giving check at your Queen's 3d square, you have
actually left your Q's Rook _en prise_! Black takes it, of course, and
having gained such an important advantage, ought to win easily.

11. Castles, (_i.e._, plays 11. Q's Kt. takes Bishop.
K to his Kt's sq., and
Rook to K. B's sq.)
12. Kt. takes Kt. 12. Castles.
13. Queen to her 2d. 13. Q. B's Pawn to B's 4th.

Your last move is very subtle; finding the mistake that Black had
committed in not retreating his Queen directly after winning the Rook,
you determine, if possible, to prevent her escape by gaining command of
all the squares she can move to. Seeing the danger, Black throws forward
this Pawn to enable him, if possible, to bring the Queen off, by playing