There's a concept in political theory about why people become nostalgic for lost causes, failed movements, etc - kind of a backwards looking utopianism? If onl

There's a concept in political theory about why people become nostalgic for lost causes, failed movements, etc - kind of a backwards looking utopianism? If only we had done X, if only this group had succeeded instead of failed in the past... I do agree that it's a way to avoid looking at the actual implementations and details of a real thing, and just go to what might have been directly.