Claim
Two variables set your pay
The first is how much value passes through your hands. The second is how hard you are to replace at that level of value. Everything else, including how many hours you work, is noise around those two.
This explains things that otherwise look unfair. A man who works brutal hours on tasks that any of four hundred candidates could do is paid by the market for the task, not for the hours. A man who spends two days a week on the only relationship that keeps a large contract alive is expensive to replace, and gets paid accordingly, even though his calendar looks lighter.
Evidence
Where the number actually comes from
Inside a company, your salary is set by a band: a range attached to a level, usually reviewed once a year against survey data the employer buys from a compensation consultancy. Your manager can normally move you inside the band and cannot move the band.
That single fact reorganizes the whole problem. Asking for a large increase within a level is asking for something your manager mostly cannot grant. Asking to be moved a level, or changing employer, moves the band itself. When you hear that there is no budget, it is often true and it is a statement about the band, not about your work.
Claim
Replaceability is about the specific combination
Being hard to replace does not mean being the best at one thing. In most jobs it means holding an unusual combination: the engineer who can also run a client meeting, the operations lead who reads a contract properly, the analyst who understands the factory floor.
That is good news, because becoming the best in the country at a single skill is a long shot, and being one of the few people in your company who holds two ordinary skills at once is a normal thing to achieve in eighteen months.
Action
Write your economic function in one sentence
Finish this sentence in writing: the company pays me because I make or protect value by ___.
No job titles allowed, no verbs like support, help or manage on their own. Something checkable: I keep the billing system running, and if it stops we cannot invoice. I bring in about a third of new client revenue. I am the only person who can price a custom job without escalating.
If you cannot finish the sentence, that is the most useful thing you will learn this week, and days 2 and 3 are the repair.
Example
Ade spent four years as a competent project manager whose sentence was, in his own words, I keep things on track. Nobody could have written a business case around that.
He changed one thing deliberately. His company kept losing money on fixed price work, so he learned the estimating model, badly at first, and started sitting in on scoping calls. Eleven months later his sentence was: I catch underpriced jobs before we sign them, which last year was about 200,000 of margin. Same person, same hours, same title. He moved two salary bands in the following year because there was now something to argue with.
Caution
Indispensable is not the same as promotable
There is a version of this that traps men. If you make yourself the only person who can operate one critical, unglamorous system, you become impossible to promote, because promoting you means finding two replacements and nobody wants the project.
The test is whether your value is in the doing or in the design. Document the system, train a successor, and keep the judgment. Men who hoard access get job security and a ceiling. Men who hand over the mechanics and keep the decisions get moved up, which is the same protection with a raise attached.
Aside
What this model leaves out
Plenty. Discrimination is real and measured, so two people with identical value and identical replaceability are not always paid the same. Some sectors are paid badly no matter how irreplaceable you are, because the money is not there: teaching and care work are the obvious cases, and no amount of skill stacking fixes a sector wide pay ceiling.
Luck matters too. The same work at a company that happens to be growing pays more than at one that is shrinking. So treat the model as the part you can act on rather than a complete account, and notice when the honest answer is that you are in the wrong industry rather than the wrong position in yours.