I interpret it like so: there are careers which require a very particular training path and careers which do not. Additionally, many training paths are widely applicable to several distinct industries.
If you graduate with a degree in math or computer science, you can work in just about any division of tech, you can work in just about any division of finance (maybe not traditional investment banking, but most analyst/trading/quant roles), you can work in certain applications of biology, chemistry, physics, astronomy, genetics or other sciences, you can work in many areas of advertising, you can work in many areas of marketing...you could start your own company, you could publish a novel...frankly you could do just about everything other than be a lawyer or a doctor.
Writing all this out, it actually sounds like the optimal career path is to get formal education and training in the most difficult or restricted fields, because you'll still have so many options anyway. Then you can cross-pollinate your knowledge in other fields.
If you graduate with a degree in math or computer science, you can work in just about any division of tech, you can work in just about any division of finance (maybe not traditional investment banking, but most analyst/trading/quant roles), you can work in certain applications of biology, chemistry, physics, astronomy, genetics or other sciences, you can work in many areas of advertising, you can work in many areas of marketing...you could start your own company, you could publish a novel...frankly you could do just about everything other than be a lawyer or a doctor.
Writing all this out, it actually sounds like the optimal career path is to get formal education and training in the most difficult or restricted fields, because you'll still have so many options anyway. Then you can cross-pollinate your knowledge in other fields.