From the foregoing it will be clear to the beginner that if a
player succeeds in winning a Pawn he can win the game if he is
able to exchange all pieces so that only the Pawns are left.
However, he will not yet see the way in which this exchange of
pieces can be forced. It is evident that the player who has lost
the Pawn will try to avoid the exchange, hoping that he may be
able to regain the Pawn with his pieces. Therefore, he will
permit his opponent an exchange only if, in avoiding it, he would
sustain an additional loss. The position of Diagram 17 offers a
simple example. White on the move will play R-e5, offering the
exchange of Rooks. If Black tried to avoid the exchange by
playing R-b6, White would capture the Pawn f5 with the Rook and
after Black's King moves out of check he would take the Pawn g4
too. Therefore Black has to make the offered exchange of Rooks,
and White then wins by advancing the c-Pawn which forces Black's
King over to the Queen's wing and leaves the Pawns of the King's
wing unprotected.

+---------------------------------------+
8 | | | | | | | | |
|---------------------------------------|
7 | | #P | | | | | | |
|---------------------------------------|
6 | | | | | | | | |
|---------------------------------------|
5 | | #R | | | | #P | | #K |
|---------------------------------------|
4 | | ^P | | | | ^K | #P | ^P |
|---------------------------------------|
3 | | | ^P | | | | ^P | |