One of the things I believe the author says about human nature is that we can be our own worst enemies. The heroine and narrator, the "new" Mrs. DeWinter (Rebecca was the old Mrs. DeWinter) starts out in the novel having a bad case of inferiority. It is understandable because she is an orphan who has not been treated with much respect for most of her life. Plus, it is Victorian England, so women are second-class citizens. Further, she has married a rather forboding man who seemingly is haunted by the memory of his beautiful and exciting first wife, Rebecca. When the heroine and narrator marries, it is only then that she is referred to by name, and it is the name of her husband - Mrs. DeWinter. Is it any wonder that this woman has low self esteem?
However, as the novel progresses, we learn that Maxim is not haunted by grief but by evil. Rebecca was evil. Her memory is kept alive by the evil servant, Mrs. Danvers. The more Mrs. DeWinter learns about the truth, the more she realizes that it is she that her husband loves, and she comes out of her shell of inferiority.
In many ways, Mrs. DeWinter is a product of her time, a Victorian woman who is no doubt thankful to her husband for giving her some security in life, but contrast Mrs. DeWinter with some examples of strong Victorian literary women such as Jane Eyre (who was also an orphan but definitely NOT insecure) or Catherine Earnshaw. I think the author also shows that humans suffer greatly sometimes over misconceptions.