Willing suspension of disbelief
The Scene: MB and I are watching season three of Buffy, the episode "Amends". After a near-hour of characters bitching about the heat in the Southern California (fake) town of Sunnydale, a lovely snowfall interrupts a big dramatic scene between Buffy and Angel.
MB: What the hell? What is up with the snow?
VBG: It's a romantic moment.
MB: It doesn't make sense.
VBG: Christmas magic, then?
MB: I still don't get it. What is it supposed to mean?
VBG: Well, snow sometimes symbolizes purity, or a clean slate.
MB: I still don't see how it relates.
VBG: There are demons living under the Christmas tree farm, and you're worried about a little snow?