a sim's aspiration is their biggest goal. you can change your sim's aspiration whenever you want. the first aspiration you choose when you are creating your sim will give you a special trait, but changing your sim's aspiration after that won't change your sim's traits. each aspiration gives your sims a set of tasks to complete. when you complete all these tasks you will get a second special trait. the trait you get will be different for each aspiration. these can be completed if wanted using cheat codes in the game.