The point is to demonstrate that if a fictional character in a work of fiction does X and it works out, that does not serve as evidence that a real person doing X will work out in reality.
Do you understand the distinction between "does not serve as evidence" and "serves as evidence against"?
Now in fact it is possible to learn from self-directed study. But your odds of learning are massively better when you get to ask questions, test your understanding by talking with others, and have your ability to explain your understanding graded.
Which means that, on average, people get more value out of going through a book in a classroom setting than they get by reading it on their own.
Whether that is enough value to justify tuition is another story entirely...