Is that the best way to sum up the question? S.L., a loyal MR reader, asked:
What is the thing that would with highest likelihood be true if you didn't know it was probably not? This is extremely interesting but also too broad to get a handle on—easier to think about in certain areas. E.g. what is the economic non-fact that satisfies this, or the physical ("god does not play dice" is up there).
I will try "that the universe as we know has not been there forever." When I was a kid it seemed obvious to me that the sky and stars had always been there, albeit with some recycling of content, much like they changed the TV shows every few years or so. I was surprised to learn about the Big Bang, at first held out hope for steady state matter theories, and now again see that some form of constancy may survive at the level of the metaverse.
How about in economics? I am surprised how little power real interest rates have to predict investment. I am surprised how few investors can consistently violate/beat the weak efficient markets hypothesis (aren't lots of people simply smarter than the marginal investor?). And I am surprised that the Industrial Revolution ever took place, after not having taken place for so long.