This is concept is a neat one that I think differentiates the real world from many fantasy worlds. In the latter, many of the core problems are built around somebody having "forbidden" or "dark" knowledge, or the heroes needing to find just the right rare answer to some kind of fundamental problem that somebody wrote down but that was suppressed. Think Horcruxes in Harry Potter sort of a deal.

In the real world, we have classification, but by-and-large those are about very specific elements of very specific things (i.e. the exact shape/location of that secondary, not that the secondary exists or that Sandia does modeling of that sort of thing). No one's really the gatekeeper of knowledge of things like nuclear engineering or biological gain-of-function. There's not really a litmus test for someone to attend to a microbiology graduate program or take a chemistry class that would enable them to develop synthetic drugs.

Same thing with martial arts; no one's hiding some secret martial technique. A BJJ purple belt will, in a fistfight, toy with just about anyone else on the planet not trained in jiujitsu like they're a toddler. And you can just, like, walk into many strip malls across the North America, pay your $200/mo, and a few years later of consistently showing up, you're there. No secret death touch or spiritual clarity needed.