Perhaps the most general and most important mental habit to instill is an appreciation of the folly of trying to draw conclusions from incomplete and unrepresentative evidence. An essential corollary of this appreciation should be an awareness of how often our everyday experience presents us with biased samples of information.

A person's conclusions can only be as solid as the information on which they are based. Thus, a person who is exposed to almost nothing but inaccurate information on a given subject almost inevitably develops an erroneous belief, a belief that can seem to be "an irresistible product" of the individual's (secondhand) experience.

we believe certain things because they ought to be true.

We may be particularly inclined to acquire and retain beliefs that make us feel good.

Because so much disagreement remains hidden, our beliefs are not properly shaped by healthy scrutiny and debate. The absence of such argument also leads us to exaggerate the extent to which other people believe the way we do.

When we prefer to believe something, we may approach the relevant evidence by asking ourselves,"what evidence is there to support this belief?"...Note that this question is not unbiased: It directs our attention to supportive evidence and away from information that might contradict the desired conclusion. Because it is almost always possible to uncover some supportive evidence, the asymmetrical way we frame the question makes us overly likely to become convinced of what we hope to be true.