User blog comment:B214/Talk About What You Want! 2/@comment-24098614-20140711002036/@comment-16281343-20140711023400

I don't think that's the reason

Cao Cao's ambition is to fight and defeat supernatural beings even though he's just a human. But that skewered because he relied on a supernatural power;  Medusa's eye.

Truth Idea is based on the ambition of the user and if he didn't implant and use Medusa's eye, Truth Idea would've worked.