Some persuasion checks are not meant to be completed. For example, if you try to persuade the troll in the bridge by using Strenght, you will always fail, because you won't intimidate a troll.
While it does makes sense, the problem is that you never know beforehand which one isn't going to work. So it's nothing but a guessing game, and therefore, bad design, because it's pointless and serves no purpose but to reload the game and try again.
