Uncertainty is in the mind, not in reality. I was going to say the Mind-Projection Fallacy, but might as well make it very specific and focused. If you can make everyone I know believe intuitively that embracing "I don't know" does not cause reality to crumble... that'd be great.
We can get to "I don't currently know" later. :)
Followup to: The Most Frequently Useful Thing
What's the number one thing that goes into a book on rationality, which would make you buy a copy of that book for a friend? We can, of course, talk about all the ways that the rationality of the Distant World At Large needs to be improved. But in this case - I think the more useful data might be the Near question, "With respect to the people I actually know, what do I want to see in that book, so that I can give the book to them to explain it?"
(And again, please think of your own answer-component before reading others' comments.)