When creating a character’s three big traits (the Inner Wound/Big Lie, the Want, and the Need), it’s important to know how these work together, and why.
The plot in your story springs from the character’s quest to resolve a conflict or problem that he or she has. (We’re going to continue to use The Wizard of Oz and A Civil Campaign. The second is science fiction.) Because the problem is inherent to only one person, that person is the protagonist and the character who drives the story.
Miles wants a wife, but he looks like a mutant on a world that loathes mutants. All the women he’s courted are offworlders. They love him, but don’t want to settle down on his home world. Because he’s the only heir to his father’s title (an aristocrat), and because he loves his world and is foster-brother to its emperor, he needs to settle down with someone who can accept becoming a citizen of his somewhat-backward planet. He loves strong and capable women, and they don’t want to move to a world where women have fewer rights. On top of that, his world had been rediscovered eighty years previously and been given modern medicine, and the previous generation used that medicine to select heavily for boys, so there are very few women for the men in Miles’s generation to marry.
He has a problem, he’s desperate, and he believes that only his incredible ability to BS and manipulate people can get him what he wants. He’s desperately afraid that any woman he can love will not love him enough to marry him. Basically, Miles is three weasels in a trenchcoat, the kind of character you can’t help but love while still never necessarily wanting to be one of his inner circle.
Big lie: He has to manipulate someone into loving him. It’s the only way.
This is one of his fundamental beliefs. It’s part of the bedrock of his personality, and it needs to change. As long as he clings to this belief, no woman he’s interested in and who can stomach living on his planet will ever want to be with him.
He happened to find a suitable woman in the book that precedes this one. Ekaterin is a native of his homeworld and in the same class of aristocrats, so she has the same sort of noblesse oblige values he does. She’s smart, principled, tough, and ambitious. Everyone likes her and she is a genuinely kind person. However, she spent ten years with a husband who degraded her. He died about a month before the story began, so she’s not ready to have a relationship or marry yet, though she very much likes and admires Miles. Miles is desperate to marry her before some other better-looking and less manic/depressive guy comes along and snaps her up.
Want: Miles wants to trick Ekaterin into marrying him. She is perfect for him, he’s in love with her, and he needs to settle down and repopulate his decimated family. She is The One. However, his approach is that of someone who is afraid that a precious commodity will be stolen, and he doesn’t believe that he can win her on his own.
If Miles gets what he wants–a wife who was tricked into marrying him–his story will end in tragedy. No woman wants to be tricked into marrying a man. That’s the sort of thing that kills love.
If your character gets what they want, it’s a tragedy. The Want is the vehicle that allows the character to maintain his imperfect, damaged state.
Need: Miles needs to be straight with Ekaterin and trust that her admiration, respect, and friendship with him will lead to marriage, or, if it doesn’t, accept that she isn’t the one for him and move on. If Miles gets what he Needs, he gets his Happily Ever After (HEA) ending. He wins. However, it’s very, very hard for a person to accept that what they need is more important than what they want, and they usually struggle mightily hard against that acceptance, which is where all the conflict in your story comes from.
And that is why almost all books have only one protagonist: the story is the story of the protagonist’s acceptance of what he wants, and the healing of his Inner Wound or the refutation of his Big Lie.
Where does the villain come in?
Here, the villain wants to stop Miles from doing anything useful, at all, and since Miles wants to marry Ekaterin, the villain targets the couple and throws in all kinds of roadblocks. Ekaterin and Miles demolish the villain together in the climax.
Sometimes the villain will mirror the protagonist–the villain may be a version of the protagonist who gets what she wants instead of what she needs, and becomes a cautionary tale. Sometimes the villain will be a metaphor for something, like in the Terminator series–in the first and last Terminator movies, the Terminator is a mindless machine, and the threat is the rise of self-aware technology. Or, in the case of the movie Alien, the villain is actually the corporation Weyland-Yutani, which symbolizes corporate greed over human life.
But if the villain is a person who opposes the protagonist because he wants to personally cause the protagonist grief, the villain will also need a Lie, Want, and Need. A good example here is Grace Burrowes’s Regency romance, The Captive Duke. The protag has built the villain up in his head to be a Great Source of Evil, and to be fair the villain is an enemy soldier and the person who held and tortured him for months. But, at the end of the book, the protag doesn’t defeat the villain. He discovers that the villain isn’t the villain he’s made him out to be. Instead, the protagonist changes his mind about what he wants, and the villain goes on to be the protagonist in the next book, The Traitor. (It was definitely interesting to see a torturer be made a protagonist in a romance novel. I read the book just to see how that was accomplished, though it’s also a smashing good read.)