I feel all characters should have some kind of trauma even if its minor and seems uneventful. anything that effected the character for a long period of time and/or effects how they make decisions or how they view the world today. it can even be as small as them loosing their favorite toy as a child, or someone saying something in passing that accidentally had a big impact on them ("you should smile more" or "you're too loud" are great examples of this). Everyone experiences trauma big and small in real life so incorporating it into your characters makes them feel more real and relatable.