Chapter 19 takes on the human tendency to believe we understand far more than we actually do about the world. The reasons for this phenomenon were highlighted earlier and are briefly recounted here. WYSIATI combines with cause-and-effect thinking such that System 1 creates an apparent understanding of reality based on very limited data and a dedication to explaining everything with causation. The halo effect comes along and lends emotional coherence to the story through a simplification that makes the characters all-good or all-bad, further reducing the likelihood that System 2 will expend mental effort to test the story.

That is, System 1 will create the best possible narrative from whatever data it has, offering apparent lessons and warnings. Most of the time, however, the narrative does not account for the large role of luck and, therefore, the lessons, warnings, and sense of understanding are not useful in the sense expected. Instead, they show how far System 1’s suggestions are from objectively measured reality.

One outgrowth of WYSIATI involves our inability to fully know how we understood the world before something changed our mind or our beliefs.