Whether you believe you can, or you believe you can't... you're right. (Henry Ford).
In the province of the mind, what one believes to be true is true or becomes true. In the mind, there are no limits.
Believe nothing because a wise man said it... Believe nothing because it is generally held as true... Believe nothing because it is written... Believe nothing because it is said to be divine... Believe nothing because someone else believes it... Believe only what you yourself judge to be true. (The Buddha)
It is always better to have no ideas than false ones; to believe nothing, than to believe that is wrong. (Thomas Jefferson)