A Sim's personality is defined by traits and aspirations. Gamers will have to select these options when first creating their household Sims, but it's not uncommon to want to change this later on in the game. While the Growing Together expansion pack added self-discovery traits to The Sims 4, which make it possible for a Sim to remove to add traits to their personality, there are ways to do this, whether gamers own Growing Together or not.