From chapter 5 of Aristotle's poetics (5.6):
Of simple plots and actions the episodic are the worst. By an episodic plot I mean one in which the sequence of episodes is neither necessary nor probable. Second-rate poets compose this knd of their own accord; good poets do so on account of the actors. In writing pieces for competitive display they draw out the plot beyond its potential, and are often forced to distort the sequence.Aristotle, of course, wrote this well before the time of Christ, meaning that critical taste in literature and drama (and, now, film) has not much changed. And yet, who doesn't appreciate a good ol' deus ex machina once in a while, or an implausibly fortunate character? Prescriptivism has its limits in literary theory as in linguistics.