Based on the series, Loki, from the Marvel Cinematic Universe

The Time Variance Authority (TVA) is a organization that controls all of time and space into a single timeline, the Sacred Timeline.

Twilight meeting her friends, becoming an alicorn: all of this was supposed to happen.

Lyra meeting Twilight on the thousandth Sun Celebration? Not supposed to happen!

Those who do what they are not supposed to do would have their branching timeline erased and themselves "pruned", or also erased.