Shu's territory is much smaller than Wei's, its economic base is much worse and its population base is much less than Wei's. Similarly, the national strength of Wei is growing much faster than that of Shu.

In the Northern Expedition, Shu's national strength was too weak .. It was also an attacker, and its geographical advantage was not in Shu. Wei's policy is "nine kinds of justice", which is very useful for uniting domestic forces. People are not on the Shu side. Fighting consumes Shu, so we can't afford it. ...

The weakness of natural national strength determines that Wei itself is invincible without chaos.