What's the difference between sane people and insane people? What exactly do insane people do? Alfred Korzybski, who developed the concept of general semantics, explains that insane people try to make the world of reality fit what is in their heads.
The insane person who thinks he is Napoleon makes the outside world fit that notion.
The sane person constantly analyzes the world of reality and then changes what's inside his or her head to fit the facts.
That's an awful lot of trouble for most people. Besides, how many people want to constantly change their opinions to fit the facts? It's a whole lot easier to change the facts to fit your opinions.
Unsane people make up their minds and then find the facts to "verify" the opinion. Or even more commonly, they accept the opinion of the nearest "expert," and then they don't have to bother with the facts at all. (Word of mouth.)
2 of Korzybski's books are on The Sherman Foundation Dangerous Ideas Reading List. I highly recommend the General Semantics Seminar. Science and Sanity is incredible but not an easy read.