This one is such a fundamental part of my soul that I can’t believe it’s taken me so long to add it to my list.

Rule 17: Be uncertain.

 
Some variants:

· Everything you know can possibly be wrong.
· Doubt and question.
· Recognize your ignorance and leave room for doubt.
· Live with a healthy skepticism for everything.
· Recognize the ignorance of experts.
· Have no respect whatsoever for the authority of experts.
· Forget who said it and instead look at what he starts with, where he ends up, and ask yourself: “Does it make sense?”

One of the great things about Wikipedia is that it teaches you to do this automatically.

 
HT: Dick Feynman