You seem to also miss that fact that there is sometimes both a relatively strong demand for a job and limited pool of applicable candidates (e.g., neurosurgery). That also drives wages up. It is a combination of the subjective value given to the deliverables for the job and the demand for the job. It is easier to replace a janitor than it is to replace a transplant surgeon. Additionally, the variation in performance from janitors is likely less than for transplant surgeons. This goes into the bidding of what people are willing to pay for such positions. It isn't anything against those who perform such jobs, it just is a reflection of how certain outcomes/deliverables are valued in a given society.