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To supplement a great answer by Faheem Mitha:

I would add that there are professions with very structured career (e.g. in medicine, law and military), and problems there are at least as severe. In general, the thing is a about the guild system, where the only way to become a professional is to get acceptance of a small community of professionals (cf. free jobs, where anyone can start and it is the market who decides).

Such systems have good quality control (i.e. there is no way around internal checks), but also generate huge gap between the already established people and the newcomers (which is an ample room for abuse - conflict with supervisors may not only jeopardize one's position in a particular company or institute, but whole career).

As a side note, internships in the guild system are not only meant to teach, but also to control supply, so to maintain prices or prestige.