Abbreviated WP
Willpower is the mental ability to endure hardship and remain in control of ones own actions. It encompasses personal discipline, self-control and pain tolerance. It is different than Courage or Maturity which are Emotional Stats.
It is the primary ability used for mental Gut-Checks. Often it is associated with psionics.
In cases of mental damage or exhaustion, Willpower is used to calculate the Grace Period and/or Damage Divisor instead of Endurance.