Self-deception : Deception of oneself, one's own person.
There is a lot of deception and self-deception in the world and in society. One problem here of a logical and psychological kind is that whereas it is obvious how and why persons can deceive other persons, it is not obvious how they can deceive themselves.
The answer comes in several steps.
First, there is no reason to believe that people are not capable of believing their own lies. Indeed, to a considerable extent this is necessary to play any social role whatsoever: You must pretend that you are a so-and-so and feel such-and-such, also if you don't think you are much of a so-and-so and anyway would like to do and feel something else, and be elsewhere.
Second, there are many ways to tamper with one's evidence and retain one's prejudices: By not reading or listening to any book, paper or argument that does not already support one's own ideas; by turning a blind eye to any event that goes against one's prejudgments; by following one's own leaders of one's opinions; by freely indulging in wishful thinking whenever that seems helpful to retain one's beliefs or values; and generally by remaining as uneducated and unscientific as one can be concerning those opinions one desires to retain.
Third, one always can resort to all manner of logical fallacies, consciously or unconsciously. Indeed, it is surprising how crude the fallacies may be in order to be accepted by those who desire to retain their beliefs come what may.
A favourite one, through the centuries, was 'my country (party, religion, authority, boss, colleagues, friends, family) right or wrong' - in short: I believe it because My Kind Of Folks believe it:
"I always voted at my party's call,
And I never thought of thinking for myself at all."
(W.S. Gilbert )
Fourth, failing all of the above one can always become a post-modernist or a relativist: Simply insist that truth does not exist at all and that all moral opinions are equally valid, and you never can be refuted and you always are morally justified whatever you believe or do. It's so easy and so satisfying!
In short, the means for self-deception are many, varied, and tested and found to work through the ages, and the motives for self-deception have always been great: Life often is painful, and it sure feels better if you deceive yourself about it.