When Creative Assembly releases a new Total war game, which has a new AI, that is capable of defeating world champion in chess in 5 turns, which uses ambushes and flank attacks in each battle, as well as luring your units into traps, makes use of neat diplomacy to unite all the world against you in the campaign, AI, that knows the weaknesses of human mind, and predicts your movements. Sometimes it pretends to be weak or beaten, just to launch a new attack, after it has fooled you. And that happens on "easy" difficulty settings.
AI also learns from it's mistakes and becomes more and more clever with each campaign, so, even if you learn to play the game very well, AI has learned even more by that time.

Yeah, you are pretty much doomed.