So back in the day I gave my students this sentence
It felt chilly after the jacuzzi.
and said what's wrong with it? We teased out the issues of not knowing what "it" was, of the fact that you can't "after the Jacuzzi" and the fact that "it felt" was wimpier than simply going for the jugular and saying "it was."
I explained that while they may have been taught to avoid to be verbs in high school (one kid stated that it was a point off for every to be verb in each paper), that there were no hard and fast rules like that in the real world, and that sometimes things just are and need to be expressed that way in order to create credible narrators.
To which a student raised his hand, "What if we want to create an unreliable narrator?"
At the time I didn't have a response and I just canned the question by telling him to save it for his creative writing classes not his comp credit.
But I've never forgotten that question.
I tell myself that if I had been more on the ball I would have pointed out the differences between an non-credible narrator and an unreliable one. That an non-credible narrator tells you things you don't believe because the reader believes the narrator is an idiot, whereas the reader doesn't believe the unreliable narrator because the reader has been tipped off that something is astray.
Notable unreliable narrators in 20th century literature: Ford Maddox Ford's The Good Solider, Anita Shrive's All He Ever Wanted, Margaret Atwood's The Handmaid's Tale. (List woefully short.)
In the first two examples there is something amiss with the narrator. The narrator starts off asserting things that we believe, but as the dissertations go on we realize that he is (in both cases) completely deluding himself as to the reality of the situation. In The Handmaid's Tale, like in many distopias, the narrator is forced into a position on unreliability not because of a mental delusion but because what limited information reaches her is heavily filtered by those in power. She only knows -- and therefore we only know -- what they want her to know.
Yet, with all of these examples, the narrator asserts what little facts he or she knows. Despite the delusions of grandeur and self-importance, all notions are presented as fact. And if we were to go by tone alone we would say they are credible narrators. They report well what they perceive without sounding wishy-washy, but as a source of information they are unreliable. Thus making an important difference between the It felt and the It was camps.