Something I find fascinating is that many of Borges’ stories demonstrate a solid grasp of fairly advanced mathematics of his time [0] but he had little formal education. I like to try imagine the work he must have put in to attain this knowledge. I think of Pierre Menard as an example of the extremal principle [1], bringing insight into how works of literature are interpreted by considering extreme cases. A good counterpart to Pierre Menard is The Library of Babel [2], also in Ficciones.
[0] https://en.m.wikipedia.org/wiki/Jorge_Luis_Borges_and_mathem...