I think it a good starting point to claim that someone would’t think of deceiving himself unless that about which he were about to deceive himself were thought to be painful for him to confront. The thought of someone trying to deceive himself about something pleasant sounds patently absurd. It could only be that someone who got a chocolate cake for his birthday were trying not to be disappointed when he says, ‘This was the kind of cake that I really wanted.’ In this case, he would have been pained to have felt that his desire for angel food cake wasn’t actually satisfied and so he tells himself instead that it is chocolate cake that he always wanted.
Self-deception does seem to be like this: telling ourselves the things we would like to believe rather than examining whether something we think or said is, as a matter of fact, true. The reason we would like to believe that the world is cheery and bright in its everyday aspect is that believing this seems to make our lives a lot easier. Isn’t it great? This is the best of all possible worlds!