As writers, we know everything there is to know about our story world and its characters, so it can be very easy to slip into the habit of narrating the story exactly as it appears in our imagination. To be effective storytellers however, we need to maintain a close handle on our narrative voice.
A key component of narrative voice is the perspective or Point of View (POV) from which we choose to tell our story. We need to maintain consistency in our chosen POV to avoid head-hopping.