Your standard movie plot generally features an introduction to a hero, a problem facing said hero and then the hero resolving said problem - it's a simple formula that has been the basis of stories since the time of Aesop and before.
However, quite how those problems are solved for heroes and villains alike can be a little bit too convenient for some viewers' tastes and really point to rather lazy writing. Enormous problems with simple solutions are nothing new but the way some of the most famous movies in Hollywood pull out the save defy belief.
It's not an issue when the convenience in question has been set up by something earlier in the film in a clever way, but when it's all just shoe-horned in uncomfortably, it's hardly a satisfying experience for the audience. That's not organic story-telling, it's narrative cheating.
And looking back over the illustrious history of film, there have been a surprising - and annoying - number of plots whose resolutions have been reliant on some pretty ridiculous coincidences. It's almost like something being convenient to story trumps the need to actually build any sense of logic...