Alternate Character Interpretation: One can read the fable with the troll as the protagonist, which can change the moral to something along the lines of "you shouldn't just keep waiting for something better to come along."
Family-Unfriendly Aesop: The grass actually is greener on the other side, patience is not a virtue, violence solves everything, and/or pass the buck if you're scared of facing a problem.
Fridge Logic: Why would the troll let the first goats pass? After they tell him that the next goat is on the way, why not just eat them and wait for the next one? Sure, he still would have gotten trounced by the third goat, but he would have died with a full stomach. We can only assume that trolls are stupid in this setting.