I suggest the above description of a main character is a recipe for an unpublished novel. While it may be true, it misses key points regarding characters who appear in well-read fiction.
First, the definition implies a disconnect between the events and the character. In page-turning stories, things ought not happen to a character. Rather, the character ought to go out and make things happen. The events aren’t centered on the character as much as the character is causing the events.
Secondly, the character as agent develops because of his wants and needs. These twin motivating passions have to do with both external and internal desires.
The external refers to something a character perceives will solve a problem, fulfill a longing, advance a goal. Harry Potter needs to attend Hogwarts, Cinderella longs to go to the ball, Dorothy must return home.
The internal has to do with an inner desires fueling a character and may be things she doesn’t realize at first. In fact these passions may be so ingrained in a character, she doesn’t understand these are motivating her. Harry Potter wants revenge, Cinderella longs to be loved, Dorothy wants to be loving.
Often a character reaches a point of revelation and comes to a place of clarity. She might then embrace what she finds or she may determine to change. Scarlet O’Hara determines she will never go hungry again, Bilbo Baggins embraces his role as “burglar,” Lucy Pevensie realizes she should do what Aslan tells her even if no one else believes her.
Internal and external wants and needs motivate the main character to action. He makes a plan and determines how he should go about acquiring what he perceives to be his greatest need. His plan may be involved, it may lead to a second plan or a revised plan, it may unfold in stages. The point is, the character is not passively waiting for things to happen to him. He is an instigator.
He is not the only instigator, however. The story also has antagonists who act. They are bent on foiling the main character’s plan or changing his intentions. They create obstacles that delay or derail his plans, causing him to revisit his goals and readjust what he’d hoped to accomplish.
Dorothy wants to go home but learns only the Wizard of Oz can help her. Her plan, then, is to go to Oz and put her petition before the Wizard. When she at last gains an audience with him, he promises to help her only if she kills the Wicked Witch of the West, giving her a new goal. Throughout the story Dorothy alters her plan and aims for something different as a stepping stone to her ultimate goal–returning home.
In essence, that desire drives the story, and the events that make up the story stem from Dorothy’s efforts to accomplish her goal. Put another way, Dorothy’s efforts are the story. The key is, whether succeeding or failing, Dorothy is striving to achieve what she wants.
She may succeed or fail in her efforts, but readers are firmly behind her, hoping the best for her because she’s active. She struggles to accomplish what she believes the circumstances require.
Dorothy doesn’t act alone. None of the characters do. Cinderella attended the ball only because of her fairy godmother’s gifts, Gandalf provided Bilbo with the help he needed to unite the Five Armies, and the Weasleys showed Harry Potter how to reach Platform 9 3/4 where he would catch the train to Hogwarts.
But the help these characters received in no way canceled out their need to struggle against the obstacles and work toward their goal. After all, that’s what a story is about.