Board Thread:General Discussion/@comment-28912103-20170122165217

So, a lot of people who played Undertale have done the Genocide route, where you go out of your way to kill everything in sight. But sometimes, they'll be confused at why sans, the final boss of the run... he doesn't stop you BEFORE you're level 19 and almost everyone's dead. Let me explain why.

Ignore the fact that this player is about to die. Look at the health bar. Notice something?

No, not the fact that it's red. To the right. That KR.

That stands for KARMA: A way of destroying your ability to be invincible after getting hit. That's why his damage hurts so much. Without KARMA on the opponent, his attacks deal nothing but one measley point of damage.

KARMA not only destroys invincibility, but it also casts lingering damage. So, if you haven't killed everyone, you won't get KARMA. And if you don't have KARMA, sans is completely powerless. I mean, you'd have to be TRYING to get killed by him to die at his hands.

That's why he doesn't come after you after realizing you killed even one person. Because he'd most certainly die. 