TO move between classes, before the 19th century was not an easy thing. People generally did not marry below them, and to do so was not considered proper. WIth the onset of the industrial revolution, however, and the trade and wealth that it brought, made it much easier for a family to go from not wealthy to wealthy. This made the gentry very nervous. They were even more critical, then, of those who had done so. As Darcy points out, the girls, "low connections . . . must very materially lessen their chance of marrying men of any consideration in the world." This gives a good background to why the story falls in place the way it does.