I understand why actors and actresses go on TV shows and promote their upcoming movies, but at some point prior to their appearance, you might think someone might say, "Hey, by the way, let's not reveal these details because they kinda spoil the entire film." Unfortunately, no one said that to Rachel McAdams yesterday when she appeared on The Daily Show with Jon Stewart, as it only took, like, one or two questions before the girl just opened up and spewed plot points from The Time Traveler's Wife as if someone injected her with a dose of truth juice.

Don't get me wrong, McAdams seems like a sweet girl and all, but c'mon! Even Jon Stewart tried to stop her from ruining everything by doling out his usual shtick, but the girl kept going and going -- it was seriously a complete trainwreck. Recently at Comic-Con, Cameron Diaz did something similar while sitting on a panel for The Box, giving away a major twist in that film, which incited a debate between a bunch of folks on Twitter wondering why these people aren't prepped before these types of appearances. And if they are prepped, shouldn't they be smart enough to know what to say and what not to say?

Which brings us to an interesting topic: How much or how little should an actor, actress or filmmaker be able to talk about their film while promoting it on television? Usually at a press junket they'll open up about everything because everyone there has seen the movie, but what sort of adjustments should these folks make when they go on, say, The Daily Show? Was McAdams wrong for giving away all those plot points, or are we just making a big deal out of nothing?

Watch the video after the jump ...