Willpower is not yet integrated into the game (Alpha versions).
Will be layered on top of many of the other systems to act essentially as a gameplay “buff”, providing you with a temporary advantage that allows you to overcome a life-threatening situation.
Think of it as a kind of mental or emotional “shield” you can call up in dire situations.
In The Long Dark, this takes the form of a Polaroid Photograph that Mackenzie has in his inventory and can refer to in times of need. When he looks at it, he is reminded of what he’s fighting for, what he has to live for.
But, with each use, the photograph fades a bit more, as though the memories that fuel it become less specific, less real.
The Willpower photo can be “recharged” in the game, by accomplishing certain goals, navigating certain choices, progressing through the story, etc. But always, you will have to use the Willpower photo very sparingly, because you never know what dangerous survival situation might be just over the next hill.