A dog cannot make this journey alone.
But maybe a wolf can.
Boris said this to Balto after he left, and I think this applies to humans as well. I think it means to humans that:
If you look at yourself as just any ordinary person, you wouldn't be able to do anything with your life. You would say to yourself, "I'm just any ol' guy."
But, if you see yourself as a great warrior, a hero, or a wolf (in Balto's case) You can do so much more, and you would be capable of so many things.