Basically, they're saying a human needs to be extremely versatile, being able to manage any challenge presented in life.
This is in a lot of ways, bullshit. Once you get a certain number of people, which isn't that many, you can get people focused on a task - amazingly, people who study a small area and practice it often get quite good at that task. Why have 10,000 people in a town who can plan an invasion (and how often would they do that?) when you can have 5 or 6 of them able to do that, and thats what they attain proficiency in?