Later in life, I started to question whether these high achieving students would do well regardless of what exam was given. (Assuming reasonable questions, of course – this rules out things like "derive Ohm's Law from Maxwell's Equations in 30 seconds".) For example, if I got to give them an exam based on things I thought were important, how well would they do? And if they didn't do well, would it matter? Suppose I was a world-class researcher/professor – would it then matter? Some people interpret the grade that a world-class researcher/professor gives as a blanket endorsement (or not) of the student, but that endorsement may not be warranted. (Recall a time I've mentioned when a physics professor flunked 60% of the MIT freshman physics students in the fall of 1978. The professor would not change her mind – the grades stood. But it is not clear that all of these students really deserved to fail, as the grading was much harsher than what it had been in recent offerings of the class.)
This also relates to my job searching during my (not so) recent periods of unemployment, where it was even less possible for me to "perfectly prepare" for the interviews. There was just far too much material to cover. It was very discouraging and frustrating having to explain to people why I was unemployed despite having a master's degree in CS, etc. "The interviews are too difficult; there is no way for me to reasonably prepare for them" was not a sufficient explanation for some people (especially who aren't in the computer field).