I believe that when imagination stops growing, so will we. After all, what is imagination but a better world which pulls us closer to perfection while keeping us from drowning in God's blinding holiness. And if we can no longer create a world better than our own, then where will we go? We will be stuck wandering in a desert- desperate for one drop of truth and yet refusing to drink.
Characters are an essential part of any story. Whether it be fiction or non-fiction, there is always a character with a story to tell. Of course, without a story to tell that character becomes incredibly dull. Even if their story is that they were un-extraordinary, at least they still have a story. Honestly, stories about un-extraordinary people tend to draw in readers when written well because they lend to a sense of identification.
Anyways, back to my main point- character development.
To begin with, there are two extremes of character development that must be avoided. The first is depression. Giving a character a fault that they can't seem to work around or some horrific story is fine, but too much is too much and too much is depressing. Everything in moderation.
The second extreme is suppression of reality. This is when a character is so perfect, so flawless, and so happy that there is nothing left to gain from there story. How can a character develop if they are already perfect in every way? They can't.
Basically, the theme of this is- everything in moderation. It is good to have some elements of joy or at least hope in a character because it give the reader hope that the story will actually go somewhere. It is also good, however, to have some elements of pain and flaw in a character so that the reader has hope that the story can go somewhere.
Remember that development is key to a strong character, but to develop-mental is to watch your story crash and burn.