The actuarial exams are some of the most if not the most difficult credential exams out there. Maybe other professions' licensing exams out there might be harder than a single actuarial exam, especially one of the preliminaries, but as a series, actuarial exams are pretty much ridiculous. It really is difficult to get a feeling for how hard it is without having to experience it yourself (that's what she said). I'm talking about in terms of who passes and fails, not the scale of individual percentages. Even in my few years as an engineer I took an exam where the highest score was in the 40-50% range, but obviously that class was curved so at least 2/3 or something of the class passed. I forget the exact wording, but here's my paraphrasing of one of the best descriptions I've read of them:
Think of a graduate level math course.
There is no teacher.
There are several books from various authors. But you don't know which one is best.
You never have class.
The classmates you compete with are some of the top analytical minds in the world.
The only grade is the final exam.
At least half the problems on that exam are trying to trick you.
2/3 of the class is guaranteed to fail.
The class is only offered twice a year.
Repeat that same process 10 times.
After the first four passes:
Add high level financial topics, insurance laws and accounting regulations to all that math.
Reduce the frequency of exam offerings to once per year.
Oh, and for each exam, you're competing with the top 33% from the previous exam.