Last time, I spoke about how our own biases often end up dominating our books if we're not careful to look at what sorts of ideas we're presenting and why. Now, in the least skilled authors, this can be overt--a character might just start ranting about some pet political notion of the author's without cease for pages and pages--but it can also come out in ways that are much harder to recognize, to the point that many readers (and even the author themselves) may not realize what kind of message is actually being sent. Let me demonstrate with a riddle:
A young boy is wheeled into the hospital, he's unconscious and blood is seeping through his shirt. A doctor runs up and asks "What happened?" The paramedic pushing his gurney says "He was in a car crash, his father died at the scene, and the kid's got a collapsed lung." The doctor then looks down at the and suddenly recoils in shock, then says "I'm sorry, I can't operate on this boy. He's my son."
Get it?