Main Character Growth doesn't happen outside of him. His "problem" is seen to be outside of him. As a Steadfast Main Character, he never addresses the source of his drive, only its external symptoms. But he still needs to grow and adapt as the story develops. Here's how the growth happens internally to a steadfast character. Let's say a family member decides to run for president. They ask for your support and you give it.

• Then you learn that the candidate/family member's platform is pro-life and you're pro-choice (or vice versa). It takes a lot of energy (justifications) for you to stay on board with that, but you do.
• Then the media begins hounding you because of your association with the candidate. This is another hurdle that requires more effort to stay the course.
• Then you begin losing friends, and business, and maybe even other family members because of your support for this candidacy. It takes monumental effort to stay on board.
• Lastly, you come to understand that others think you must be a will-less wonder, conditioned to do whatever the candidate wishes, and deaf to the terrible things said about the candidate. This brings you to a breaking point. But if you can find that last bit of stamina, you stay the course and hope for the best.

You see, the pressure on a Steadfast character, and a Change character for that matter, changes its nature from act to act. So the effort in one area does not work in another, and more (and different) effort must be made. Character Growth is never a straight line.