Frustration is not knowing if you are doing something wrong, the quest in question is bugged, or it's just one of 'those' quests and it's going to take a bloodbath to complete.
The one making me irritable right now is Dragon Quest IX #067 Nab the Knife-Nicker. You have to put a Shivery Shrubbery to sleep, then kill it with Toxic Dagger.
I can one shot them with Toxic Dagger, no problem.
I can snooze them.... about half the time (which is obnoxious in and of itself.)
And I have killed 34+ of them (one whole mana bar from my dagger user plus a few) with NO quest item dropped.