A story begins with two things. It needs four or six things (depending on how you like to count).
1) A protagonist,
2) an antagonist (who can be a villian),
3) directly conflicting goals between the two characters,
4) and motivation for them both.
I recently wrote a short story that went through a lot of revamping and rethinking before I got very far. My main character, Valerie, started out as a bounty hunter almost in a corner, choosing to fight instead of run. But she didn't care if she lived beyond the battle.
That is a weak, inactive protagonist. Not interesting to read (and a pain to write if you want to make the story go anywhere). My flaw was pointed out to me (I'm looking forward to the day I catch on quicker—or just stop making this error), and I rethought.
Okay, so Valerie wasn't who I thought she was. So who was she?
She needed a goal, yes, but she had that. Survival. It just wasn't strong enough. But wait, survival can be a very strong goal. What was missing? Motivation. She needed a reason to want to live. She needed a reason to want to take out the man hunting her.
This was my "Aha" moment. Or, if you prefer.
She needed a motivation behind her goal. That's not something I've heard explained much in my writing classes—at least, not in that wording. But it's one of the most necessary aspects of a protagonist, or any developed character. The why behind the what. And the answer? It had to do with a relationship. Relationships are always on the line in a story, the only question is which one. Then why that one. And, of course, how. Once you answer those questions, you're rolling.
I answered them. I answered the why she needed to survive with two relationships. A boyfriend. And his daughter. (It just became more interesting in your imagination, didn't it?) The answer to why those two relationships and how they're on the line has to do with the antagonist's goal and motivation. See how it all ties together? Before my eyes (...okay, twas all in my planning head) the story was building in strength. I had a goal with motivation for my protagonist and had further developed the direct conflict of goals with my antagonist/villian.
Now the story had heart. There was purpose to Valerie's actions. She had a reason to care enough to pursue her goal, and pursue it she did. Ta da.
So, a story needs...
1) a protagonist
2) with a [strong] goal
3) that's backed up by [deep] motivation,
4) and an antagonist/villian
5) with a [strong] opposing goal
6) that is also backed up by [deep] motivation.
Now you know why.