Developer: "Get the BAD ENDING."
Requirements (2 Options): Ether Lose the game to the raiders (You can't defend a raider attack), or let them in when they knock.
Difficulty: Easy Or Medium
Tip:
1. Raiders will come depending on how often you scavenge. Ted and the family will write "We might sound Paranoid... but we think we were followed.." when someone returns from a scavenging mission. Eventually, when you are choosing to start a scavenge there will be "Gun shots and ___ can only mean one thing... raiders are above us..." (or something similar to this). This means the Raiders are here
2. When given the chance to "attack the raiders" (Your weapon option will be an Axe or Gun) don't choose ether and just ignore it. If you do this you can freely scavenge since the raiders have retreated (You want them to stay).
3. Your difficulty makes the raiders attack often or rarely (This was recently added and raiders are more aggressive on higher difficulties thanks tot he 2020-06-18 patch!).
4. If you decide to go for the "knock" ending. I don't recommend you go for any other ending, ignore the Military, Twins, Cat, and Mad Scientist ending. Only open when the raiders are roaming around the area.
UPDATE (Everything above has been edited thanks to this great update): A Patch was released today and this achievement has FINALLY been fixed! This is now possible to get! 2020-06-18