Suppose I’m working on pulling out some functionality from a large, monolithic application. How much am I making my company?
Issue 1: It's very difficult to tell if your contribution got 50% improvement in performance because there were 10 other devs pushing in features and bug fixes. This is the attribution problem
Issue 2: This happens over time. It's very unlikely that your 50% improvement happens every year or month. Because, think for your self, this is compounding with large rates. It grows quickly. 1.5x improvement in 6 cycles (months or years) is 10x. This essentially is the time problem
Issue 3: even if you deliver the results you did, in a large company there's a large bureaucracy and no one person has the ability to increase your salary by that much. This is the control problem.
It’s avtually fairly non-trivial to be able to say with even a modicum of certainty how much value a given developer brings to their company.
I currently write software used by millions of people. Partly because I’m a backend engineer, I have no real idea how much more the company is making due to my direct efforts. Since they keep paying me, I’m assuming it’s a decent multiple of my carrying cost, but I have no way to measure it.