In these last days, God has sent a strong delusion to the fools of the world for not accepting the truth. According to Plato, the worst kind of lie is the "lie in the soul". This believes a lie when deep down you might suspect the truth but you resist and believe in that lie anyway. No one really wants to be deceived and a person doesn't deceive one's own self on purpose, but the fact remains that self-deception is the most common type of delusion.
Saint Paul wrote of the grand delusion in his second letter to the Thessalonians. The day of the Lord shall not come, except there come a falling away first, the Anti-christ be revealed and,
With all deceitfulness and unrighteousness in them that perish because they received not the love of the truth that they might be saved. And for this cause God shall send them a strong delusion, that they should believe a lie: that they all might be damned who believed not the truth but had pleasure in unrighteousness.