There’s not even close to a one-size-fits-all approach to Christmas tree decor. Some people have aesthetically-pleasing themes, with refined color schemes and clear design choices. But I’d say that by and large, most Christmas-decorators have a motley crew of tree hangings: collected on travels perhaps, or handmade by young relatives, personalized in mall kiosks, or gifted by friends with inside jokes in mind.
Ornaments are often small tokens of “I thought of you,” made more special by the comparatively short time they’re put on show. They’re a way of giving someone a hyper-personalized gift, and because they only come out once a year, some of the pressure (both to give and to display) is mitigated.