What the plot requires

Of course, it annoys me when movie and TV plots require people to do things that aren't credible.  Roger Ebert famously used the term "idiot plot" to describe a plot which requires the characters to be uniformly incapable of perceiving something that's perfectly obvious to non-idiotic moviegoers from the start, lest the central problem be solved too soon.  One example, I imagine, is the Princess Diaries sequel (directed by Gary Marshall--who else?) where Anne Hathaway's mother the Queen wants to marry her off because she's worried about a pretender to the throne, who happens to be male, single, young and handsome...  I haven't even seen the movie, but I think I can already guess how things will work out.

One thing that definitely bugs me is plots that require a character to be careless at a crucial moment.  There was an episode of THE WALTONS where Jason was considering becoming a conscientious objector and discussed it with a recruiting officer.  Just as he was leaving and a couple of guys were coming in to volunteer, the officer added, "I hope you talk to your parents ABOUT BECOMING A CO." (My emphasis.) Of course he could have omitted the emphasized part, but then the guys coming in wouldn't know enough to bully Jason shortly afterward.

Another example is Spike Lee's JUNGLE FEVER.  In that movie Wesley Snipes confides in his friend (Lee) that he's cheating on his wife.  Soon after Snipes comes home to find his wife throwing him out.  It turns out that Lee was careless enough to tell his wife about it, and the latter promptly informed Snipes' wife.  Don't tell any secrets to Spike Lee!

If one thing bothers me more than a plot that requires a character to be careless, it's a plot that requires a character to be childish!  The whole plot of Lee's SUMMER OF SAM requires John Leguizamo to be a philandering, hopeless douchebag. (Lee's characters tend to do whatever the plot requires.) Other such characters are Tom Cruise in EYES WIDE SHUT and Julia Roberts in several romantic comedies.