Why did Sima Yi laugh at his son Si Mazhao when he found out that he wanted to withdraw his troops?

In the novel Romance of the Three Kingdoms, there is a scene that is very impressive. At that time, Sima Yi mobilized troops to attack the street pavilion, but after sending spies, he was worried that this was another trick of Zhuge Liang, because Sima Yi had been defeated by Zhuge Liang many times before, so he was very cautious when dealing with Zhuge Liang.

But his son, Si Mazhao, thought it was a piece of cake to capture the street kiosks. He found that the man stationed here was not Zhuge Liang, but Zhuge Liang's disciple Ma Su. He is an armchair strategist. After setting up his position in the street pavilion, he didn't expect that the water source here would be cut off by the enemy. After Sima Yi visited the position for the second time, he found that Zhuge Liang was absent, which must be the enemy's flaw. Sima Yi also cut off the enemy's water source by encircling the whole mountain.

At that time, Sima Yi was really scared by Zhuge Liang, so he was careful in everything, so he was laughed at by his son Si Mazhao for being too careful. In fact, Sima Yi was defeated by Zhuge Liang many times in The Romance of Three Kingdoms, but his son Si Mazhao was born without fear of tigers, because he didn't compete with Zhuge Liang at all, so he didn't understand Zhuge Liang's strength.

But at that time, it was indeed a wrong choice for Kongming to send Ma Su to guard the street pavilion, because the street pavilion strategically sent an armchair meat steamed stuffed bun to beat the dog, and Sima Yi quickly seized this mistake after discovering that Kongming had used the wrong person and recaptured ideal city for the battle of Wei.