In a sense, effective story-based roleplaying is all about facing up to your actions. Everything you do has consequences after all, so it should be the same for the characters in a roleplaying game world.

The GM, besides creating the game world and applying the game rules, needs to make sure that your characters have to face the consequences of whatever they choose to do. Most of the time, hopefully, that's good consequences, because you've done the right thing and succeeded in defeating evil, completing the quest, slaying the monster, or whatever. But when a PC does something that logically leads to negative effects, or something that can come back and bite them later, it's the GM's job to make sure that the characters have to deal with those things later on.

If the GM doesn't enforce this form of PC karma, the game can devolve into a free-for-all, where the PCs can do anything without having to think about what they're doing and worry about the effects their actions have on the game world. From afar, it might seem petty or vindictive, but applying consequences is the way to make a game world and the people who inhabit it seem real to the players, rather than just a background for them to show off against.

Although that doesn't mean you can't also have a little fun.

Transcript

Cliegg Lars: Shmi was distraught when you murdered that Greedo boy...
Anakin: {angry} She's my mother! I love her! I'd do anything to look after her!
Cliegg Lars: But you won't face up to your own actions.
Anakin: My actions? You're the one who let her go! Why aren't you out looking for her?
Owen Lars: There are Sand People in the desert. It's not safe to leave the farm.
Padmé: Sand People?
Owen Lars: Yes. They used to be a peaceful, meditative race, until about ten years ago, when they mysteriously acquired weapons and started shooting at pod races.
Owen Lars: They began terrorising town dwellers, claiming some sort of broken promise. They've descended into barbarism.
Cliegg Lars: And we have no way of knowing which direction Shmi went. I'm afraid she's most likely dead, son.
Padmé: Wow. I wouldn't like to be the one responsible for that.