We must understand that no one has deceived us as often as we have deceived ourselves. It is precisely when we believe we cannot be deceived that we are most vulnerable to deception.
One reason for this tendency is confirmation bias. Once we hold a belief, we look for evidence that supports it—and, of course, we tend to find what we are looking for.
The key is to question our beliefs. The ones we cherish most are the ones we must examine most critically. When something feels off-limits to question, it becomes dangerous, because if it is wrong, we have no way to correct it.
One way to overcome self-deception is not to try to prove our beliefs right, but to try to prove them wrong. In other words, take the opposing viewpoint and attempt to argue for it. You will quickly discover that alternative perspectives have reasons behind them, and some of those reasons may even be stronger than your own. This openness creates the possibility for change, growth, and even enlightenment.