Sima Yi laughed at Zhuge Liang's lofty goal, but in the process of realizing it, he didn't know how to deal with the situation. Although the Shu army is fierce, it is not to be afraid. In fact, Zhuge Liang is not ignorant of contingency, but Shu Han is cowardly and afraid to gamble. Sima Yi's remarks were only to stabilize Cao Wei's morale, not to say that he had a plan to kill the enemy.
Guan Yu privately launched the Xiangfan War, which brought many disasters to Shu Han. First Yiling lost 700,000 soldiers and horses, then Liu Bei died of illness, and Liu Chan became the master. In the case of constant internal troubles and foreign invasion in Shu and Han dynasties, Zhuge Liang was unable to save the overall situation no matter how powerful he was. After Zhuge Liang was worshipped as a strategist by Liu Bei, he made such achievements with Liu Bei, which is enough to show that his ability is not as incompetent as Sima Yi laughed at.
There is something boastful in Sima Yi's words. When Zhuge Liang led the troops to the Northern Expedition, Sima Yi never took the initiative to fight. It stands to reason that Cao Wei's military forces are far more than Shu Han's, so he should go out of the city to meet them. As a result, Sima Yi has been avoiding the war. How can he lead the troops to destroy Zhuge Liang? Although Shu Han regained some troops in those days, the total population of the country was only a few hundred thousand. At this time, Cao Wei sent troops to raise fields instead, with 400 thousand foot soldiers. Therefore, Zhuge Liang is at a disadvantage in quantity.
Moreover, it was impossible for Zhuge Liang to go to their lair when he made an expedition to Cao Wei. As Sima Yi said, there are as many as one hundred thousand Shu troops. At that time, Cao Wei could completely attack the whole army and destroy Zhuge Liang. At this time, Sima Yi boasted that Zhuge Liang had fallen into his trap and could defeat Zhuge Liang himself. If he really has the talent to destroy Zhuge Liang, why didn't he lead troops into battle, but he had to endure the shame of Zhuge Liang dressing women? Because Sima Yi knows that even if the whole army is out, it may not be Zhuge Liang's opponent.
Later, Zhuge Liang really died, and Sima Yi dared not lead the troops to kill him because he was afraid that this was Zhuge Liang's plan. Zhuge Liang is dead, and Sima Yi is still so afraid. He once said that it was a slap in the face to destroy Zhuge Liang. Later, Sima Yi was ridiculed as "Zhong Da was born after Zhuge died". In fact, Zhuge Liang's failure in the Northern Expedition was lost to heaven, not to Sima Yi. If God can give him more life, it is hard to say whether Sima Yi can laugh at the end.
Conclusion: Sima Yi didn't dare to confront Zhuge Liang head-on, so he had to use the method of guarding the city as a rogue, which consumed Zhuge Liang's retreat without rations and Zhuge Liang's death. When Sima Yi wanted to establish the prestige of Cao Wei, he could only boast that he had defeated Zhuge Liang, otherwise others would look down on him and he would lose the right to lead the army. Although Sima Yi is talented, he is far from Zhuge Liang, so Sima Yi's evaluation of Zhuge Liang is a bit boastful.