Browsing your lore collection is much easier when it is organized. A simple single-layer organization scheme (whether a formal taxonomy or a folksonomy) is suitable for small amounts of lore (<100 pieces?), but a multi-level hierarchy will pay off once your collection of lore grows sufficiently large.
If possible, you should use a design that supports a piece of lore living in multiple categories at once (a directed acyclic graph rather than a single tree). A simple example: a dog can be an animal, a pet, and a patient for a veterinarian but not all dogs are pets, vet patients, or even live animals (think CatDog or Huckleberry Hound). A directed acyclic graph structure better supports representing the complexity of the world. Software engineers have long experience with directed acyclic graph structures (a Unix filesystem without symbolic links is a DAG).