This isn't forbidden knowledge, it's just not correct. People learn and grow with experience. Some projects can't afford to support many, or any, people in that

This isn't forbidden knowledge, it's just not correct. People learn and grow with experience. Some projects can't afford to support many, or any, people in that growth stage. But lots of projects can afford it, and the investment in their growth makes sense. I think it is probably also true that some people never become competent enough for many projects, but in my experience that is diminishingly rare, whereas junior developers who are still developing their skills are extremely common (unsurprisingly, since more and more people enter the field constantly).