Elizabeth Bishop generally wrote about specific people and incidents. (She also wrote often from her dreams, but I am going to ignore that fact because I don't believe the following poem is from a dream.)
For instance I recently learned that her amazing poem, Visits To St. Elizabeth's, was about visiting Ezra Pound during his time in that mental hospital. I had always thought that it came from her visits to her mother who had lived in a mental hospital until her death after Bishop was out of college. (Yes, I know the poem says a "man" but I still thought it was about visiting her mother.) But now I learn that she never once (or so they say) visited her mother there.