Character Purpose

I have been contemplating character purpose lately.

As a key part of characterisation, most people would agree that a character needs to have some desire that propels them - a driving force for their actions. In a more classic sense, a Quest in which they are searching for something. Of course, not everyone agrees with this theory. Some writers, while noting this element of storytelling, choose to do the opposite and leave the character a blank slate in that department, perhaps with a quirky personality, but pretty much pushed around by the forces of their world. Not my favourite type of book, although enjoyed by a certain breed of stylists who throw darts at plot structure.

Robert McKee, in his book Story (and seminar series), talks about conscious and unconscious desire. If any of you have run into McKee before you would know he is an advocate of structure with a capital S. In McKee's view, a character must follow a conscious desire. If they, perhaps through self-revelation or temporary defeat, abandon this desire, it must be because having delved a little deeper they have found their true desire (which they had not realised until this point) or their unconscious desire (which of course is now a conscious one).

I would have to say I agree with McKee completely on this point, but then again I absolutely hate books where the character is at the whims of their world and makes no attempt to solve their own problems or make their own way.

There is one important distinction. I like the heroic journey, but a character can be firmly driven by their purpose and yet ultimately fail without invalidating the story. It's not fun, maybe it is not heroic, but it is consistent storytelling that does not betray the reader's expectations where the character is concerned (although it stands a good chance of disappointing them).

What do you think? Does a character always have to driven by a clear desire/purpose/goal?