We think, each of us, that we're much more rational than we are. And we think that we make our decisions because we have good reasons to make them. Even when it's the other way around. We believe in the reasons, because we've already made the decision.

Suppose you like someone very much. Then, by a familiar halo effect, you will also be prone to believe many good things about that person - you will be biased in their favor. Most of us like ourselves very much, and that suffices to explain self-assessments that are biased in a particular direction.

When people believe a conclusion is true, they are also very likely to believe arguments that appear to support it, even when these arguments are unsound.

I have always believed that scientific research is another domain where a form of optimism is essential to success: I have yet to meet a successful scientist who lacks the ability to exaggerate the importance of what he or she is doing, and I believe that someone who lacks a delusional sense of significance will wilt in the face of repeated experiences of multiple small failures and rare successes, the fate of most researchers.