We simply don't have the capacity to store the memories of our lives chronologically. Therefore, we group them according to subject matter, and that is what allows for stream of consciousness writing, as illustrated by Welty. She begins on one subject, abandons it, as returns to it later. It works this way in other media also. Movies have flashbacks to fill in missing information.
Songs return to their refrains.
Novels leap backward and forward in time as they so choose. It is easier to tell stories as you remember them. Plus, it makes more sense, as we are able to see the connection between one passage and the next, as opposed to the isolated important incidents that make up a life. Welty bends time to her advantage. I think that everyone has a story to tell.