Smoking: God hates it too! Buffy: I told one lie I had one drink Giles: Yes, and you were nearly devoured by a giant demon snake. I think the words "let that be a lesson" are a tad redundant at this juncture. In the land of television, morality and justice are swift, sure, and anvilicious. Okay folks, listen up: many of the dangerous behaviors in life are as insidious and widespread as they are because most of the time, nothing bad comes of doing them.
If you don't wear your seatbelt, most of the time, you'll be fine. It's just that on the rare occasion that you do get into a car crash, without a seatbelt, you will likely die a bloody, painful death.
So on a lot of shows especially those aimed at children , every time you do something bad, justifiable or not, you will get punished. Typically within the same episode. On a Sitcom , this isn't usually all that big a deal, except during the Very Special Episode. In a teen drama, it's a recipe for tragedy. Drive drunk even once and somebody is going to die. Have premarital sex even once and there's going to be an STD or unwanted pregnancy note although logically, there can't be an STD unless at least one of the people has had sex before, except in the less-likely-to-be-used case of being given one non-sexually via birth, blood, or other causes.
This may be accompanied by introducing characters who have been getting away with the bad thing for a while — but once the main character tries it out, things will immediately go wrong.
This trope may be used simply because it's a good way to end a particular story, or an author's personal fantasy or something, and not as a deliberate way to get any message across. The problem with this kind of lie is that it can backfire.
