I vaguely remember a book I read probably more than 5 years ago. For some reason I think the author is a famous female fantasy/sf author (but I am not 100% sure)
The story follows the main protagonist and we often see things from his perspective : it is about a bum who is a very "paranoid" magician, trying to hide in a big city and avoid using magic, very careful about the way he acts and proceed in his life to avoid drawing attention on himself(?).
The city itself is quite modern and "normal" (like a regular US city, with mostly regular people, albeit maybe a bit grimmer than real life cities?)
He has a very peculiar set of "routines" or ways of acting, every day, and has almost no money on him at all times. He sees magic in a lot of things that ordinary people would overlook/not notice.
I vaguely remember that he has something in his possession (a luggage?) containing something that has magic and that "calls" him.
The tone of the story is very paranoid, and quite grim and dark (that person's life is miserable and he always feels in danger). I think he thinks he is the last magician (? or one of the few?) and is trying to avoid someone/something (linked to that luggage in some way) that is more and more threatening.
heavy spoiler below: this may ruin the whole book experience for you if you haven't read it yet : do not click unless you already read the book
And it turns out he is just a paranoid person thinking he is a magician ? or a real magician that someone makes believe he is just paranoid? ... My memory is very weak on the particular. Whatever it was, it is hinted throughout the book but really apparent at the end.