There're plotholes, and then there're glaring plotholes. Most works have plotholes, because it's rare that the producer thinks of everything. [http://tvtropes.org/pmwiki/pmwiki.php/Main/TheProducerThinksOfEverything] On the other hand, you have movies like Frozen, which made me yell at the movie at the very end when
Granted, then there wouldn't be a movie, but my opinion is that if your entire plot revolves around your cast being dumber than a bag of rocks for most of the movie, you should probably write a better plot.
Elsa realizes that the key to controlling her power is love. This is known to the trolls, who told Anna that it would take an act of true love to cure her frozen heart problem. But the entire problem could have been avoided had they just told Elsa that at the beginning of the movie instead of focusing on warning her about what would happen if she gave in to fear, thus guaranteeing that she would live in fear her entire childhood.
Granted, then there wouldn't be a movie, but my opinion is that if your entire plot revolves around your cast being dumber than a bag of rocks for most of the movie, you should probably write a better plot.