I have found this very interesting essay from Sckott Berkun: #60 – How to be a free thinker
This is what Neuro Linguistic Programming (NLP) calls beliefs. Your beliefs define what you are, and you can never say a belief is true or false as they are constantly changing.
You should always try to make your beliefs coherent with your principles, otherwise you may face an internal battle that can destroy you. This often happens when you work for someone that has different principles than yours, and makes you act against your principles.
So I could not agree more with Scott that you should constantly question your beliefs and change the ones that do not suite your purpose at that particular moment in life.