In an interview with BlogTalk Radio, Chris Huntley describes the nature of the growth a Main Character goes through within a story. To summarize:
When a Main Character comes into a story with baggage, they’ll never be able to recognize those issues themselves. Even if someone came up to them and said, “Hey buddy, you know what? This is your problem…” and then started listing out their grievances, the Main Character would still not be affected. It won’t work because to them those issues are concealed from them. Because of this blind spot, they’ll be much more focused on the symptoms of the problem rather than the problem itself.
Therefore the process of a story allows the main character to grow in such a way that those blinders are removed so that they can see the source of their troubles. They still have to choose, “Was I on the right or wrong course?” but at least now they see it. If they stay the course, then they’ll forge forward and see if things will work out for the better or for the worse. If they decide to take a different course, they’ll have to fundamentally change and try a new approach. Again, this change offers no promise of success, it could be that they were on the right course all along.
Without that development, a story won’t seem real or natural. And this kind of change does not happen in a vacuum. If the Main Character was all alone, there would be absolutely no reason for them to confront these issues. They need some outside force or person to deal with that personal issue. With this character in place, the main character’s growth will progress naturally and the story will resonate much more strongly in the minds of audiences.