User blog comment:Ixarising/High School DxD Dream Battle/@comment-24421137-20140114074119/@comment-16281343-20140114080335

Samael's poison that Shalba brought wasn't meant for Issei, but its for Ophis.

Let's say that he can use his brain but his god complex will make him think that Cao Cao is some useless human that won't be able to hold a candle against a descendant of a True Maou.

While Cao Cao is the type who will research everything that will help him in his fight against his opponent.