Missing traits

@escapedpolarbear  Learning three traits through the Observant reward, then not learning any others, is normal.  Sometimes using "get to know" will reveal another trait, although it's not reliable and often reveals a favorite color or food (in the thought bubble) instead.  Discussing a specific topic will often help too, for example discussing art should reveal that another sim has the Artistic or Can't Stand Art trait.

The Personable charisma achievement increases a sim's chances of learning traits as well, and family members' traits count towards the total.

Learning traits through conversation is pretty random, but if you know the other sim's traits, whether through an interview from a journalist or law enforcement or from peeking another way, you can steer the conversation however you want.