If you need to employ N other tradespeople to earn a high income, that means that the ratio of high-income to low-income tradespeople is semi-fixed. If you need to have 9 employees to get 100k income, that means only 10% of the people entering the field will have a chance to earn 100k. In addition, unless N is 2 or 3, it cannot be the case everyone gets a chance at higher incomes in their life; that they will earn lower salaries the first few years but then start earning high salaries when they move up.

So, what is N? Unless it is a low number and almost everyone earns high salaries after a couple of short years, we are doing the next generation a great disservice by encouraging them to get into careers where they destroy their bodies for the benefit of the boss, not themselves.