A Hard Nut to Crack

Back in high school, a friend told me that our upcoming math test was going to be a tough nut to crack. I pointed out that it actually most likely wouldn't be that hard to crack, as it was more than likely no more than a few pages, so it would be a fairly simple matter just to rip the paper - but then he probably would have a hard time at getting a good grade if he were to do that. Some people just aren't very good at taking tests.