User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-179.232.72.234-20150227020141/@comment-1359322-20150227021818

"Truth Idea's effects depend on God's will in the Holy Spear and absorbs the wielder's ambition of this spear, and by responding to how strong the opponent is, it will create many effects and miracles which will be different depending on what the will chooses such as granting an absolute power to destroy the opponent or a blessing to the opponent to capture their hearts."

Long story short, Truth Idea takes in the will from both its wielder and the wielder's enemy and decide which one is better. Cao Cao lost that 1 because he diverted from his ideals while Ise strongly follows his ideology.