I have two Sims who've written 40+ novels each. Despite the phrasing of the badge, "Have your Sims write 80 novels", I didn't get the achievement.
So I had one of the Sims write 80+ novels. I still didn't get the achievement.
H80r1g1n It's odd that this achievement didn't trigger, but one question I have is whether you were playing while signed in at the Main Menu, so you could see your badges (and other online features) while playing. With some achievements, I noticed I didn't get credit for anything that happened offline even though the game should recognize the progress.
If you want to cheat to get the badge (since you've already earned it legitimately), you could use NRaas Retuner to set the length of your preferred type of novel to something short—maybe 20 pages or so—then max your sim's motives through a cheat or mod and let them go to work. I'd suggest a new save just to keep things simple. Let me know if you're interested and need more help with the process.
Yes, I was signed in at the time while playing via the Main Menu, and was able to check on my badges in-game.
I'm not sure yet that I want to go the NRaas Returner length. At least not soon, since it was a major investment having my Sims write all those books.
H80r1g1n All I was saying was that if you wanted to try again to get the badge, you could use Retuner to significantly cut down on the amount of time it would take your sim to write all those books. Whether you want to go that route or not, I'd suggest having your main sim write a few more books just to see if the badge triggers a little late.
