The multiverse exists because of branching caused by key decisions in the time-line, on that theory you can never correct your own time-line merely create alternative time-lines. So with MM Harry becomes aware of the multiverse and how it works, in the TT book Harry gets to engineer a world where he can win the BAT, the one he is actually in, but cannot for example save Karrin as that creates a different timeline to which he is not native, and one which may not survive the BAT, saving Karrin may create a time-line where he doesn’t defeat Ethnui or one where she dies 5 minutes later in a totally different fashion. Now that would be cruel, Harry constantly going back to BG to save Murphy only for her to constantly die a warriors death in each of the parallel words created, and Harry has to watch it, time after time.
No one tell Jim.
