I think that there is much within this question to analyze. Certainly applying the concept of ennui is a part of it. Where I think I would have to place some emphasis is on the assertion that Flaubert's work reflects the modern vice of ennui. There are two items in this assertion that could stand to be fleshed out a bit. The first would be how Flaubert views ennui. I don't think he sees is as a modern vice, as a morally inferior or substandard choice. Rather, I think that he sees it as an inextricable part of the modern setting. Emma and Charles, amongst others, are trapped by this condition of ennui primarily because they are crushed by the weight of their dreams. It is a condition of boredom that prompts them to dream or to envision something that is so very opposite of their existence. This dream animates them and drives them to embrace a course of action. When the inevitable bottom drops out because the weight of expectations was far too much for that bridge to bear, ennui sets in because of the failure to appropriate the world in accordance to their own subjectivity. Flaubert does not see this as a sin, or some type of indulgence. I think he sees it as a necessary part of the modern setting where freedom and individual autonomy is present, but happiness is not. The second point here would be whether ennui is a sin, at all. I find it very difficult to label ennui as a sin because of its effect on the individual. At its very basic, sin is something that represents indulgence, a sense of primal satisfaction. If nothing else, it feels good. To put it bluntly, ennui doesn't. It causes more depression to the individual with its result of boredom and perpetual dissatisfaction. Prior to analyzing this in other texts, I think that a discussion about whether or not ennui is a sin is in order.