although you're quite right that JA thinks the choice of a marriage partner is fundamentally a *moral* choice, and therefore one that says a lot about the character of the chooser, she also admits the possibility that good people can make good-faith mistakes. There are no perfect people in the novels, and some people with good qualities are in some pretty awful marriages -- Mr. Bennet, Sir Thomas Bertram, Mr. Palmer, Charles Musgrove (hmm. . .Is it always men? No, there was also Anne Elliot's mother. . .) There are also some marriages that it's a little hard to know about: for instance, what's going to happen with Jane Fairfax and Frank Churchill? (Didn't JA write somewhere that she thought that one wasn't going to work out?) Also, at the end of MP, the narrator tells us explicitly that if Henry hadn't run away with Maria, Edmund would have married Mary and Fanny would eventually have accepted Henry. All of which suggests, IMO, that she thinks there's an element of luck involved -- you can't always be absolutely sure how time and circumstance will change, or further illuminate the flaws in, the person you've chosen. Anne Elliot herself suggests her understanding of the contingent nature of these matters in her final verdict on Lady Russel: "It was, perhaps, one of those cases in which advice is good or bad only as the event decides."