[jltsiren]

Most people end up being employed. Therefore most hires are average. A lot more people believe they are hiring above average candidates than actually do so. Good employees are rare, for any meaningful sense of the word.

There is also another common fallacy: you measure what can be measured easily and then use the data to make conclusions about what you would have wanted to measure. For example, you measure the performance of an employee and use that to make conclusions about the success of the hiring decision. But to actually determine that, you would have to know how well other candidates would have performed in the role, and how the presence of the chosen candidate (would have) affected the performance of everyone else. Among many other things.

That's also a big part of the reproducibility crisis in science. It's impossible to make justified conclusions from data alone. You can rarely measure what you actually wanted to measure, and you never know if you took every relevant factor into account. In order to make conclusions, you have to assume a model of the system you are measuring. Then your conclusions depend on the assumption that the model you have is a useful description of the system.