Cao Pi was right to choose to sit on the mountain and watch the tiger fight, but he didn't expect the battle to develop too quickly, so he missed a good opportunity to make a move.
When Liu Bei led the Shu Han army to attack Eastern Wu, the momentum was like a rainbow, and Eastern Wu failed one after another after the sudden rise of the war, and only had the power to parry, and even faced the risk of extinction. At that time, Liu Bei's strength was indeed above that of Eastern Wu, otherwise he would not have killed Wu.
The Cao Wei court also thought so, so when Sun and Liu had not yet won or lost, it was the best way to choose to sit on the mountain and watch the tiger fight. When the battle situation is clear, Cao Wei will choose to take advantage of the situation to destroy Wu or Shu, and he can reap the benefits of the fisherman.
If he rashly attacked before the war situation became clear, it would be easy for Sun Liu to call off his troops and make peace and turn his head against himself, and if so, then Cao Wei would face an unfavorable situation. Therefore, Cao Wei sent additional troops to the front, but he remained on the sidelines, waiting for Sun and Liu to fight to the death and lose both.
However, the battle situation developed too fast, and no one expected that the little-known Lu Xun would light a fire in Yiling, which greatly damaged Liu Bei's vitality. Cao Wei also reacted quickly, preparing to attack the rear of Eastern Wu when Lu Xun attacked Sichuan and Shu. However, after the Battle of Yiling, Lu Xun did not continue to chase after him and did not give Cao Wei too many opportunities.
Cao Wei saw that Dongwu was prepared, guarded against them, and turned his head to attack Shu Han. However, after the Battle of Yiling, the Sun and Liu families were once again reduced to the weaker side.
Both sides were also aware of this problem, and Dongwu did not choose to fight Shu Han with Cao Wei, but came together with Shu Han again. Therefore, Cao Wei did not receive the benefit of the fisherman in this dispute. To put it bluntly, it was the situation that developed too quickly and beyond people's expectations.