Epistemically: I don’t personally like the concept of “intention”, but it’s part of the definition of a lie - you’re lying when you say something that you know to be false, with the intention to deceive. As such an unfilled promise would not be a lie if you intended to fulfil it when you promised it.
Morally: I think that the distinction doesn’t matter because intentions don’t matter, nor they can be assessed anyway. What matters is the harm that you cause. You said something, other people relied on it, it turned out to be false, that’s it.
Epistemically: I don’t personally like the concept of “intention”, but it’s part of the definition of a lie - you’re lying when you say something that you know to be false, with the intention to deceive. As such an unfilled promise would not be a lie if you intended to fulfil it when you promised it.
Morally: I think that the distinction doesn’t matter because intentions don’t matter, nor they can be assessed anyway. What matters is the harm that you cause. You said something, other people relied on it, it turned out to be false, that’s it.
Philosopher Hans-Georg Moeller: A Critique of Sam Harris’ “The Moral Landscape” (~1 hour)
His book: The Moral Fool: A Case for Amorality