In 1954, Ralph Ellison told the Paris Review* that a character’s development must proceed through three states: from purpose, through passion, to perception^.

The beauty of this construct is that it demands action. And action is the stuff of story. No action = no story. A character will, by their very creation, exist; however action will give the character purpose, a reason for existing. Through further action the character will declare their passion – their want – the target of their desire. Finally, out of this character’s action, and reaction to conflict, will come a perception, maybe even an epiphany. The character will be reinvented, forever changed. The character will be unable to return to that early state of simple purpose even if he wished, for purpose and passion are permanently altered due to the new found perception.
An example would be good here, but you don’t need me for that. Think of your favorite novel or short story. Think of Huck Finn or Goldilocks, think of your favorite TV show or movie. From purpose, through passion, to perception – it is right there.
It’s why you love that story.

*I am slowly reading all of the interviews in the Paris Review backlog. They are all available online. http://www.theparisreview.org/interviews. I am glad I got an MFA. Reading these I feel like I’m earning my doctorate.

^Ellison says in the interview that he is quoting Kenneth Burke.