A Skill was essentially something one earned, or it came as a privilege from the world.
In both cases, they represented a special ability that a person possessed. Usually, Skills were meant to evolve, not disappear from a person. Since Skills were an intrinsic part of a person—especially those earned—they were a permanent addition to the individual.
Skills, in a sense, could not be created nor destroyed.
… But Rey was an exception.
By using [Merger], he essentially bent the rules a little. He broke down Skills and used them to mold new ones, or more advanced versions of one.
This, in a way, was still following the rules… but teetering on the edge.
However, the complete breaker was [Sacrifice], which caused the permanent loss of Skills, changing them to Stat Points.
In this case, the nature of the Skill was changed into another kind of power—Stats.