Saving Throw
Source Player Core pg. 422
When you're first exposed to the affliction, you must attempt a saving throw against it. This first attempt to stave off the affliction is called the initial save. An affliction usually requires a Fortitude save, but the exact save and its DC are listed after the name and type of affliction. Spells that can cause an affliction typically use the caster's spell DC.
On a successful initial saving throw, you're unaffected by that exposure to the affliction. You don't need to attempt further saving throws against it unless you're exposed to the affliction again.
If you fail the initial saving throw, you advance to stage 1 of the affliction and are subjected to the listed effect. On a critical failure, after its onset period (if applicable), you advance to stage 2 of the affliction and are subjected to that effect instead.
On a successful initial saving throw, you're unaffected by that exposure to the affliction. You don't need to attempt further saving throws against it unless you're exposed to the affliction again.
If you fail the initial saving throw, you advance to stage 1 of the affliction and are subjected to the listed effect. On a critical failure, after its onset period (if applicable), you advance to stage 2 of the affliction and are subjected to that effect instead.