On the last (Sir) Michael Parkinson Show, he interviewed actor Sir Michael Caine and asked him for advice on acting and why he was so successful.
Michael Caine replied that the audience could tell if you were just saying your lines and then thinking about what you had to say next while you waited for the other person to say their lines. He said you had to listen to what the other actor was saying. “You must react to them,” he said.
This could be interpreted as being the same for writing. The author must be involved with the story and the characters to the extent that she/he reacts as her characters would as she writes. If she doesn’t feel what her characters are feeling, if she’s not gripped by the scene unfolding under her fingertips, then her story and her characters will not ring true and will not capture her reader’s interest.