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If gratitude and esteem are good foundations of affection, Elizabeth's change of sentiment will be neither improbable nor faulty. But if otherwise—if regard springing from such sources is unreasonable or unnatural, in comparison of what is so often described as arising on a first interview with its object, and even before two words have been exchanged, nothing can be said in her defence, except that she had given somewhat of a trial to the latter method in her partiality for Wickham, and that its ill success might, perhaps, authorise her to seek the other less interesting mode of attachment. Be that as it may, she saw him go with regret. (46.24)
This is one of the few times that the narrator just comes right out and tells us what principle of life is being debunked. Here, for example, it's the idea of love at first sight, which is clearly for Austen a far inferior idea than don't judge a book by its cover.