Rarity
Everything in the game is labeled common, uncommon, rare, or unique.
Common things are ubiquitous or trivial and assumed to be easily accessible. Players can play common races, acquire common items, feats, and spells, and play common classes without restriction beyond what's in their descriptions and costs.
Uncommon, rare, and unique things, however, require GM approval on a case-by-case basis. Uncommon things can typically be unlocked with a simple short-term aspiration to go looking for them.
Rare things require a long-term aspiration and unique things come up so rarely that they're typically only available if specifically ascribed or offered by the GM and not upon player characters seeking them out.
In Aether Spira, all Calling, Resurrection, Summoning, and Teleportation effects are considered rare and they require the use of Waypoints to function.