How are people's incomes determined?

When people leave school and enter the labour markets, they can choose various jobs, some have higher incomes than others. What makes different jobs have different income levels on average? There are many factors determining a job's income level.

Firstly, the jobs which require long period of training and practice (including education) usually have higher incomes than those which do not require much experience. This is very obvious and intuitive as the supply of such labours is relatively limited. Doctor is a classical example of such that being doctors requires years of learning and practice. Secondly, the jobs which potentially experience moral hazards are likely to be paid higher incomes in order to make them moral in practice. For example, bankers are paid higher because they have access to enormous amount of money and high incomes can reduce the risk of moral hazard (as the expected returns from financial frauds are reduced). Thirdly, the jobs which have influence also tend to be paid higher. For example, pop stars have influence over their fans, which create values for other parties, such as advertise firms. However, technically speaking civil servants and politicians also have enormous influence over others, but they receive relatively lower incomes, given their experience of training and practice (civil servants and politicians are usually social elites in the society). This is because of social value. In most societies, civil servants and politicians are treated as jobs where people voluntarily contribute themselves into national services. Moreover, respect and future higher incomes are given to these jobs as some form of compensation to their current relatively low incomes that many civil servants and politicians gain positions in the private sector after their political career, for example, the former Chancellor George Osborne was given a position in BlackRock which is the world's largest asset management firm.

A job's wage level is determined by the supply and demand of a job.  A movie star earns a lot of money; however, the supply of actors and actress does not seem low, but actors and actresses are often required to have specific skills and looking, which strictly limit the supply.