> People who fit into the Shell Silverstein "I'm so good I don't have to brag" bucket aren't as visible because they're working, not talking about working.

It isn't as much as "talking about working" but putting the bulk of their effort in self-promotion.

If you hire someone because they excelled at self-promotion, the reason you hired them is because they excelled at self-promotion. Not because they are great or even good, but because they are good at convincing the likes of you to hire the likes of them.

In business settings this sort of problem ends up being a vicious cycle. Anyone that hires a self-promoting scrub is motivated to make that decision look like a success as well, otherwise the scrub's failure will also be their own failure. If these scrubs output passable work instead of great or even good, that's something you as a manager can work with.