I often feel that we fall into a trap of believing that we must provide a driving goal for a main character at the outset. And yet, as I look at compelling fiction, main characters do not have the same simplicity of a single defining characteristic as does the supporting cast. Main characters are main characters. They are complex. There is room to explore their inner conflict. We are often in their point of view, and everything--the entire world--is seen through them.
At the end of the day none of us 'real people' have single goal--life is messy. And so, distilling a main character to one goal seems like a bad idea.
A few examples:
The main from How to Stop Time. He purportedly wants to 'find his daughter.' Well, he's doing nothing about that. He's lived for 500 years without taking out a single want ad or filing a single missing person's report.
Frodo. Does he want to carry the ring? I don't think so. If anything he wants the ring. The ring 'wants' more than Frodo does.
Harry Potter wants his parents. That's stupid--they're dead. On the other hand Dobbie, a rather two dimensional character, wants to keep Harry safe and also wants to be free.
Luke Skywalker wants a bunch of stuff, in just the first movie. To save the princess. To kiss the princess. To join the rebellion. To master the force. To blow up the death star. Etc.
The protagonist in A Fault in our Stars either wants the boy, or wants the boy to live, or wants to meet the guy that wrote the book she likes (and the boy likes too), or wants to live herself. I'm not sure. Love the story, though. What is the girl's initial want? I could not tell you.
What does Rose want in Titanic? Jack? To rebel? To get away from the man she is engaged to? If the answer to this example is that her want changes through the story, then what is her initial want?
The Martian may be the clearest example of a main character 'want' and driving need. He wants to get back to Earth. Funnily enough, all he can do is survive. (And he does a fantastic job at this.) Getting back to Earth requires everyone else.
I understand that 'character' has room to develop (and wants have room to change), but the idea that we must shoehorn stories into a main character that has one driving want (or even one starting want) seems counterproductive to good fiction.
Question: Does it really serve a main character to give them one driving want? Please explain why, or why not.