We love protagonists because they “protag,” as Brandon Sanderson puts it. Protagonists are dynamic and experience growth, or at least change.
In his BYU lectures on sci-fi/fantasy writing, Sanderson points to three areas that protagonists can grow to create a compelling arc: competence, likeability, and proactivity. In Star Wars, Luke grows in competence, while Han grows in likeability and proactivity. Leia is arguably all three from the beginning.
Is this schema contrived? Maybe, but most good fiction is essentially contriving situations to manufacture emotion. I find it a helpful way to check in about which characters are growing in what way, while at the same time recognizing that, along with growth in competence, likeability, and proactivity, characters can experience all kinds of less obvious sorts of change and growth.
Jacob N. Given 