I always listen to audiobooks before sleeping, this sounds interesting so I will listen to this tonight.
Although likely incorrect, I must take a guess on the three things..
Religion
The ego
Emotions.
I want to say education as sometimes we think we know for a fact things regarding our areas of expertise, we refuse to contemplate ideas we have been taught were otherwise.. But education teaches critical thinking, so it can't be that.
RE: Social Critic Jacques Barzun Told Us it Would Be This Way