To unlock this achievement you have to go through the winter without losing anyone in the process... It might be harder than it sounds, but if you are having trouble you can create your own story to make it easier !
From the menu select
Write My Own Story and then choose the desired options.
Recommendations:2 People (1 for scavenge / 1 sleep - guard) less mouths to feed :)
Days Until Ceasefire: 20Intensity Of The Conflict: LowWinter Comes: EarlyWinter Harshness: MildWinter Length: ShortWith these setting i manage to unlock it in on
Day 7. Good luck !