People are much more complicated in real life, but my characters are as subtle and nuanced as I can make them. But if you say my characters are too black and white, you've missed the point. Villains are meant to be black-hearted in popular novels. If you say I have a grey-hearted villain, then I've failed.

This quote means that the author is trying to make their characters as realistic as possible, with complex personalities and motivations. However, some readers may miss the point of what the author is trying to accomplish and comment that the characters are too “black and white”. The author is saying that when it comes to villains, there should be a clear distinction between good and bad, and if the villain is portrayed with any sympathy or ambiguity, that is a sign that the author has not done their job properly.