Basically what it says in the title
I remember reading years ago in some chapter of what I think is a Kurt Vonnegut book, that the Germans have a word for someone you meet who represents who you could become, but would prefer not to, and how that person is significant as a symbol and drives you to become who you should be or want to be.
Did I dream this? What book was it and what was the word?
You might be thinking of Übermensch from Nietzsche’s Thus Spoke Zarathustra. The term doppelgänger is close in that it looks like one’s self, but it usually isn’t considered the best version of that person.