I'm thinking they went to work, performed work, and were compensated in accordance with the supply and demand for their experience and knowledge or special skill set.
aka - a white collar professional
However, you're assuming that the market is efficient and rational. What if it is irrational?
For example, let's suppose that a CEO drives his company into the ground and is compensated with a $50 million golden parachute. He obtained the CEO job because he knew people on the Board of Directors. In contrast, what if an MBA who also had a science PhD and was brilliant but had poor social skills could have and would have happily done a far, far better job for a mere $500,000/year?
I suspect that much of the income white collar professionals earn may be tainted by that kind of market irrationality and inefficiency. There is no shortage of people with professional degrees who would happily work those high-paying jobs for less money and do just as good of a job. However, employers like to discriminate against people who end up unemployed or underemployed-and-out-of-field and don't like to create lower-paying entry-level jobs for people.
I don't buy the dogma that highly-paid white collar professionals are really all that amazing or hard-working or unique or irreplaceable, at least not today when we have huge oversupplies of people with advanced degrees and professional degrees.
Part of the problem is employers and businesses collective refusal to train new people so that they can acquire experience in these fields resulting in a small supply of people who are experienced. I'm not convinced that the shortage of experienced people and the value placed on experience is a result of the free market at work and not some sort of irrational breakdown in market forces (akin to the problem of information asymmetry). Fix that problem and the supply of qualified employees would be such that high white collar wages would drop. God knows--Americans will fall all over themselves to train for high-paying positions, which is why far more people apply to medical school than there are spots.