Answers:
From what I have found it is considered to be a cliche and an expression that has been around for ages and used by many people. It is also considered to be advice that can be ignored. If you want to write about something that you do not know about you can; just do research and then apply your experiences to it.
When I first read your question I thought immediately of John Dewey. While I do not think that he coined the expression, he did explain that children relate what they learn to the things that they already know and if they know nothing about the topic (have no life experience in it) then they have difficulty learning the material.