When I was young, I was taught that how much you earn is proportional to how hard you work (more hours, more labour intensive etc)

Show graph of how hard you work + income

After some time I realized it's about the value of your work (how much income you bring or cost saving to your employer / client / society) . Investment banker earns exponentially higher than others because the value he generates is tremendous when filing IPO for a company (from zero value to public recognized price point)

Show graph of patio11 that one

But if you look at those super rich people, billionaire, it's about the perceived value of work, or value of their company in this case. Note that it is perceived value, which is how others think how much their value might worth, not the actual value the company brought as actual value is very difficult to measure. Moreover, market is always determined by perceived value by others.

Company valuation by other investor

A company won't voluntarily pay you more out of kindness in any circumstance. They pay you $x amount of monthly salary because they know or predict they can earn extra more $1.5x (or more) per month by hiring you to do stuff. It's cliche but the primary goal of a business is to make money, else its a charity or hobby.

Apple pays $200k+ annual salary to its employee, it's one of the highest figure in Silicon Valley. This figure might seems insanely high for us but if you look at their annual revenue per employee, its $2 million per employee. Which means if Apple are paying $200k per employee, they get 1000% return per employee, which is an extremely good investment, of course Apple would be happy to pay $200k per employee if they are bringing 10x return.

But why can't Apple pay their employee lower? Like maybe $100k per year so that it would bring more money to investor and making itself richer? Of course they can do it, but if they do so their employee will probably resign and flock to Google or Microsoft for higher pay hence Apple will compete the wages with Google and Microsoft. This is market in action, there is a finite demand for engineer from company and there is a finite supply of engineer. If the demand for engineer is high but supply is low, company will have to pay higher to attract them since other company will pay highly too. Unless all these company conspire to fix the price, that's a difference case, which we call price fixing.

If you are looking for a job, think of yourself as a product in a market. You are selling yourself as an employee to company (employer). The salary you requested is the price of a product, what ultimately determine your asking price is the value you can provide (perceived to provide, not actually provide, but usually close to it). If an employer is confident with the perceived value you provide, you have higher chance of getting hired.

How to increase your perceived value? Think of what can you bring to the table, skill set, knowledge, good personality, etc. If you have a proven previous record, it's even better, that's why company will often ask for resume/CVs.

Perceived value is also constrained by the supply and demand of the workforce. Few decades ago there were not much university graduates and they were perceived as really smart people and were paid highly because there is very few supply but the demand is there. Nowadays almost everyone is a university graduate, you can throw a brick randomly and it will almost certain hit an university graduate. Every university fresh graduates are competing for the fixed amount job demand, since most of them bring similar advantage to the table, in order to make themselves stand out they will have to start competing on lower price / salary. It's a race to the bottom, making employer happier and employee suffer, there will always be another graduates willing to take on the job with a salary lower than yours.

Another way to increase your perceived value is to work in an industry which the demand is high but the supply is low, such as programming (yes, even more specific in mobile, ops, machine learning), plumber, carpenter (Yes, this might sound surprising but with the rising amount of graduates, some traditional demanded skill set is slowly phasing out hence lesser supply) etc.

tl;dr : To increase your earning, bring more to the table and especially to a table which has high demand but low supply.