[dragonsngoblins]

Well a lot of the time when you are looking at something you are trying to diagnose some problem or another, which means you want to be 100% sure of what something is doing. Even if the function provides a good abstraction you might still want to make sure that it is doing exactly what it says on the tin because you are desk checking some weird behaviour and you want to make sure each step is acting correctly

[fiddlerwoaroof]

Agreed, but that means you verified that the use site was correct and are now examining whether the abstractions it depends on were implemented correctly.

My point is just that you shouldn’t normally have to keep both sides of a call site in mind at once.