Many professionals are trained, by necessity, to often make quick, informed decisions and be confident in those choices. It's not surprising this bleeds into the rest of their lives.
In a more general sense, I've come across this too with individuals who have independently acquired "expertise", but whom dropped out of college (or high school).
For example, some niches where I have came across a lot of know-it-all types without much (if any) formal education, are:
- self-taught musicians
- drug dealers
- self-taught computer hackers (who never went to college)
- fitness trainers
- etc ...