I've been taking a few classes lately, to make my self more marketable, that I think everyone should take at some point. Especially if you're a writer.
Granted these classes are aimed at making yourself more marketable to the rat race. But They look at what can be changed in human behavior to bring about a desired result. As a writer you have two uses of that. What most writers think of first off is, of course, characters. And you're right. But even more so, the writer can benefit for themselves.
For instance the class I had today was about reworking your thought to a more positive fame. As writers we deal with a lot of emotions and a lot of bad things happening to good people. It's called conflict, our bread and butter. And if your not careful you can let all that conflict tear you down as a person. DON'T! Take a break if your working on some depressing scene and go do something goofy. Just be down right silly. I dare you to say 'rubber baby buggie bumpers' to the mirror with a mouth full of marshmallows and and not at least smile at the result.
And as for characters, they too can benefit from your understanding this. If you have a character who is looking at life through ash colored glasses, change just a few words of theirs and see the difference.
For instance. Our brains don't process the word don't on a basic level. In higher realms we understand the concept of refraining from something but not in our core thought process. If your character is saying "I don't care about the world." they are conflicting their brains and causing a kind of depression. Because at the basic level their brain hears "I care about the world." but their higher processes get conflicting info. You can show your characters progress by having them put more active phrases into play. So "I don't care about the world." becomes. "I care more about god than the world." Or something like that.
See how the second one causes movement in your thoughts where the first is static?
I'm going to be working more of this into both my writing and my life. Give it a try yourself and let me know how it works for you.