Okay, folks, you read it here first: leave your common sense at home.
Nobody said any such thing, so please resist the temptation to build strawman arguments.
There is such a thing as "common sense". It's roughly what would be commonly apparent to someone reasonably well-versed
in a topic or field of endeavor.
People often leave out the reasonably well-versed
part, and substitute a kind of "I am smart/cool/awesome/tough enough to figure it out without actually knowing anything" attitude. This is often little more than a thin veneer of bluster painted over a surface of raw ignorance.
Tell me this: do any trainers ever recommend another trainer or another school?
Many do. It's hard to miss that if you look into the subject much. I know that James Yeager, Gabe Suarez, Rob Pincus, Tom Givens, Travis Haley, Chris Costa, Mas Ayoob, Paul Howe, Larry Vickers, Dave Spaulding, and a whole host of lesser-knowns have been quite open about this. Many make it a point to train with other companies several times a year.