It was once widely believed that for the body to be healthy, it needed the right balance of “humors”: black bile, yellow bile, phlegm, and blood. That was partially right, but mostly wrong. We don’t believe that model any more.
It’s always valuable to reassess common knowledge. That is the heart of human progress.
Even so, the number of people in the comments asking for book recommendations on fitness and nutrition shows that many people here would rather cling to their comfort zone of digging deeper. You can re-evaluate words on paper all day, but it will never, ever compare to the understanding you get from actually trying the thing you want to understand.
How is asking for book recommendations an indication people are not willing to dig deeper? An intellectual approach to exercise is highly advisable. Yes, you can become too extreme and never end up actually exercising, but conversely a lack of knowledge can lead to poor outcomes depending on your goals.
It’s always valuable to reassess common knowledge. That is the heart of human progress.