Nobody ever stays the same, were always changing. The same thing should go for your characters. Realistic stories depend highly on character development.
If we have a protagonist that stayed the same through the whole story, then your in serious need of revision.
Writing a book has steps you have to follow, creating the plot, changes in the plot and also changes in the characters. Plot changes will obviously affect the character. So its only logical that it creates real fundamentals changes to their personality, emotions and worldview.
It doesn't what kind of book you need character change. It would be a disservice to your book.
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Writing Without Cliches
RandomIt's not enough to love our story ideas. We need to weigh their suitability as subjects for fiction, and then figure out how to go about making use of them. This means steering clear of cliché and its sappy cousin-melodrama.