Trait (The Sims 3)
Traits are like atoms of personality that you can assign to your Sims. You combine them to create complex personalities. There are about 65 Traits to choose from. When you assign Traits to a Sim, that Sim will look and act the part. Toddlers, Children and Teens get a new trait at their birthday. If children had a good childhood, then you can choose a trait. If not, the game will give them a random one. They’ll have unique behaviors, preferences and advantages. Some traits give you special abilities. They can be useful to improve skills and to get special interactions.
Young Adults and up have 5 traits, Teens have 4 traits, Kids have 3 traits, Toddlers have 2 traits. The less traits a Sim has, the less complex that Sim's personality will be. For example, giving a Sim the Kleptomaniac trait only will result in him constantly stealing while giving a Sim 5 traits will result in more balance. A Sim can acquire more traits also. In fact, they can acquire all traits that don't contradict each other.
Traits are genetic and what occurs during pregnancy can affect what traits are passed on. The parents also help pick the traits. For example, bad parents don't get to pick their own traits and will have randomly assigned ones, these are generally unfavourable.
The Lifetime Reward "Midlife Crisis", costing 20 000 points, allows the player to re-choose a Sim's traits.