belief bias

If a conclusion supports your existing beliefs, you'll rationalize anything that supports it.

It's difficult for us to set aside our existing beliefs to consider the true merits of an argument. In practice this means that our ideas become impervious to criticism, and are perpetually reinforced. Instead of thinking about our beliefs in terms of 'true or false' it's probably better to think of them in terms of probability. For example we might assign a 95%+ chance that thinking in terms of probability will help us think better, and a less than 1% chance that our existing beliefs have no room for any doubt. Thinking probabalistically forces us to evaluate more rationally.

A useful thing to ask is 'when and how did I get this belief?' We tend to automatically defend our ideas without ever really questioning them.

Further reading
Wikipedia | Thinking, Fast and Slow (Please note this is an Amazon Associates link)