novel - What is the Purpose of an Inner Conflict?

I've long known what the purpose of inner conflict is. Indeed, it was one of the simplest concepts for me to grasp when I was learning about it. Now I'm not so sure.

I seem to have developed a dual understanding of inner conflict: what I used to know, and what I now know. Neither seem wrong, but they are different and can't both be the purpose of inner conflict.

My question therefore is simple: What is the purpose of inner conflict? Why does one include it in their characters?

The reason I'm not explaining how I view inner conflict is because I don't want to turn this question into a debate over which of my views are correct, or if either are. I want to hear how you view inner conflict instead.

Note: As with any aspect of writing, I'm sure there are those who disagree with it. If you believe writers should not use inner conflict, I am interested to hear what you have to say. However, please put it in a comment. Only use an answer to answer the actual question.

Answer

Inner conflict is the whole enchilada. All good stories lead up to a moment of crisis in which the protagonist must make a choice. That choice must be personally difficult. It must come at personal cost. Deciding to buy the Chevy rather than the Ford is a choice, but not one that comes at a personal moral or psychological cost. The climax of a story is always that moment of change or revelation when the protagonist must ask themselves, am I this sort of person or that, am I willing to pay this price or not?

All stories also need something to bring the protagonist to this crisis point. This is the role of external conflict. But external conflict is not enough in itself. Its point is to create the occasion on which the inner personal conflict must be faced. Otherwise resolving the external conflict is a mere technical matter, like choosing between the Chevy and the Ford.

The crisis point of inner personal conflict can also be reached without an external antagonist, without an external conflict. But external and internal conflicts are not alternatives. Internal conflict is always at the heart. The external conflict is merely a mechanism to bring them to that point.