I've heard it as "If all you have is a hammer, every problem looks like a nail".

A quick google search attributes various forms of the quote to Abraham Maslow (Presumably of Maslow's Heirarchy fame.)
--
JimFive

"I have learned the novice can often see things that the expert overlooks. All that is necessary is not to be afraid of making mistakes or of appearing naive."

Abraham Maslow, (1908 - 1970) American Psychologist