I recall years ago reading about the success formula for television sitcoms: the plots can, and often should, be completely implausible, but they must be probable. In other words, the situation and actions can be as weird as you like—the weirder, the funnier—but the sequence of events has to make sense within that weird context. Lucy wandering lost in the New York City subway with her head stuck in a mammoth loving cup was perfectly acceptable, and hilarious, so long as Ricky didn’t suddenly materialize inexplicably out of nowhere to rescue her.
This formula makes me think of my favorite movie, Alfred Hitchcock’s North by Northwest. To me, it represents the culmination of Hitchcock’s genius: a realism so rarified that it presents completely unbelievable situations in ways that make them seem perfectly natural.