My name is Max Rebuschatis and I am one of the engineers of our love letter to y'all - The Sims 4 Simulation.
Animation, design, modeling, and engineering all collaborated to create a fresh, exciting, and detailed take on our beloved virtual people.
There is surprising complexity in this system, and it is my pleasure to discuss various facets of the tech.
I'll start with a couple examples:
Did you know that Sims do, in fact, have an innate handedness? We determine the handedness of a Sim based on their unique id and roughly 75% of Sims are right-handed! This affects their default pickup hand and various other animations where mirroring is available.
Ever wonder why Sims will walk some distance to eat near other Sims? We have a sophisticated scoring system that bakes a large number of preferences into meters, which then allows us to compare routing to different objects directly while including things like object types and relationships.
Feel free to ask me anything you want about the simulation tech in this thread. I'll do my best to answer as much as I can within reason.
Note: this discussion was originally in Technical Discussion, but this seems like a more appropriate place for it. You can see the original discussion here: http://forums.thesims.com/en_US/discussion/782786/simulation-tech-talk-i#latest