In complex works of literature, it may not be as obvious. Becky Sharpe is one of the main protagonists in Vanity Fair, but she's extremely flawed. By the end of the book, she's almost unlikable. In this way she's a very good example of another truth: the well-written protagonists are round characters. They should be the most interesting, complex characters in your book or story. Becky Sharpe is by far more interesting than Vanity Fair's extremely good Amelia, and for this reason, the story's primary center of gravity remains Becky Sharpe.