Nevertheless, a cashier is not responsible for the magnitude of the cash in their till at the end of a shift. They just ring up what the customers chose to buy. And the number in the till also includes the procurement cost of the food that went out the door. The cashiers are necessary for the business to operate, but they are not directly responsible for the revenues coming in. They are counting up the dollars, not delivering value to the customers. I don't go to the grocery store to chat up the cashiers; I go to buy a variety of foods in less-than-wholesale quantities. A store with robot cashiers is still able to function, whereas a store without food on the shelves is completely pointless. The cashiers are therefore responsible for the slight preference I have for human cashiers over robot ones. I might choose to pay $5 more on a $250 grocery order, to have a live person ring it up for me, and that's the value the cashier provides, not the whole $255. But the grocery store doesn't know how much I'd pay for cashiers. I keep it secret, because if they knew, that's what they'd charge me for it, and I'd lose the value that I currently enjoy from getting that included in the price of the food. So that value is not measurable. The store would rather pay the cashiers a fixed rate, and price their added value into the cost of the food.

The oil-driller is not responsible for the price of the oil that was pumped that day. They are responsible for the cost of the holes and pipes between the reservoir and the surface, and the cost of the workplace injury insurance, and the cost of environmental damage. Those numbers can be measured. A great safety record is worth a measurable amount of money. Drill bits and mud have a measurable cost, and using less than the predicted numbers translates to an amount of money. Government fines for spills and groundwater contamination are known quantities. The geologist is the one that finds the oil, and the explorer is the one that proves it's actually there, and the refiner distills and cracks it into usable goods. Dividing up the responsibility for each barrel is hard, but counting the cash that comes in when the barrel goes out is easy.

It's not possession of the cash. It's the responsibility for delivering the value, and the measurability of that value.

An employee that brings in a contracted rate for each billable hour is responsible for delivering exactly that much value to the customer. Other people involved in the business may provide value, such as by increasing the rate beyond what the direct-value employee could otherwise negotiate on their own, or by procuring more customers, to increase the utilization rate of the direct-value employee, or in increasing productivity so that it's possible to deliver that much value per billable hour. But that's not as easily measured. The support employees deliver value to the worker that delivers value to the customer.

And that's why the direct employee doesn't ever get all that they bring in, minus the business expenses to support only them as an employee. That number isn't all them. It might not even be mostly them. But they're the ones closest to the number that can be measured. They're the ones that could most easily shed all the dead weight at the company, and strike out on their own, if they had the moxie, sacrificing some of their billable hours to do their own support and development work, to make sure that there is a contracted rate to bill the hours to.

The 1/4 to 1/3 rule is a concession to the fact that indirect-value employees are still responsible for delivering a lot of value, that indirectly increases the revenues of the company. And that represents a good balance in a medium-sized company. Smaller companies have fewer support employees. Larger companies have more dead weight.

Cashiers and oil-drillers are not relevant, unless they are on contract from another company.