"Ainsi, ce général est habile dans l'attaque dont l'adversaire ne sait pas ce qu'il doit défendre ; et il est habile dans la défense dont l'adversaire ne sait pas ce qu'il doit attaquer."

Simplified Meaning:

When someone is really good at attacking in a fight or competition, they make sure their opponent is confused about where the attack will come from. This confusion makes it hard for the opponent to protect themselves. Similarly, when someone is very good at defending, they make their opponent unsure about which point to target, making it difficult for the opponent to strike successfully. Imagine you're playing chess. If you cleverly move your pieces so that your opponent can’t predict your next move, it becomes tough for them to plan their defense (like where to move their pieces to keep their king safe). On the flip side, if your opponent doesn’t know which of their pieces you’re aiming to capture, they struggle to come up with a strategy to protect those pieces. In real life, this idea can be used in business or personal competition. If you keep your plans secret and act unpredictably, your competitors will have a hard time keeping up or stopping you. For defending, if you keep your weaknesses hidden or make yourself seem stronger everywhere, it will be tough for others to find a way to defeat you.