What is the general quality of a person who has the ability to face adversity?

The ability to face adversity is most closely associated with strength. This quality involves not just physical endurance but also emotional resilience, mental fortitude, and the capacity to overcome challenges. A person who can navigate difficult circumstances typically demonstrates perseverance and steadfastness, embodying the strength of character necessary to confront and work through hardships.

Valor, while similar, often connotes bravery in challenging situations that may involve risk, usually in a more physical or heroic sense. Power is a broader term that can refer to influence or authority rather than an individual's personal resilience. Flexibility implies adaptability and changeability, which are important traits, but they do not specifically encapsulate the enduring quality of facing and overcoming adversity. Therefore, the most accurate descriptor for someone who can confront and surmount life's challenges is strength.