Do not believe in something simply because you have heard it or because it has been handed down for many generations, or because it is found written in your religious books, or merely on the authority of your teachers and elders. Only believe after observation and analysis, when you find that anything agrees with reason, and is conducive to the good and benefit of all, accept it, and live up to it.

- Buddha

Our reason is our best guide to what is true. Authorities usually repeat what they were taught and frequently do not even believe what they profess. I would modify the statement:

Do not believe something simply because you heard it, or because it is written, or because it was handed down for many generations, or because of the authority of its proponent. Believe something only when, after observation, and critical analysis, you find that it agrees with your reason and your cosmology, and make all beliefs tentative, pending further evidence and thought.

-SCM