Principle of Two weaknesses
The principle of two weaknesses is an important principle you should always know.
In chess, besides checkmate, you should also be creating weaknesses, which will lead to advantages, which in turn lead to checkmate and a win. Sometimes, you will create a weak pawn, backward pawn, or take over weak squares. But the problem is, the defender might be able to hold on! defend it with all his strength. But if you can continue your attack, and continue to create weaknesses, then you can create a second(or more) weakness, which will stretch his defenses even more, and probably so much they will break down and you will win. It is a good principle to know in all phases of the game.
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