The most difficult subjects can be explained to the most slow-witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of doubt, what is laid before him. —Lev Tolstoy, 1897
What's up with the epigraph?
Was Tolstoy predicting the 2007 housing market crash way back in 1897? Possibly, because this quote is the perfect encapsulation of the subprime crisis.
Throughout The Big Short, we see incredibly smart people make incredibly stupid decisions based on shortsighted assumptions. That's why everyone ignores Eisman's warnings: they can't fathom that the subprime mortgage market will collapse, because they've already convinced themselves that it could never happen. Based on what evidence? None, really.
If nothing else, you should walk away from the book will some healthy skepticism about your own beliefs, as well as some willingness to adapt to changing circumstances.