Pride and Prejudice insight?

Only a little help here: I'm reading A Jane Austen Education - and the author covers this pretty well. The part I remember well is that Elizabeth 'feels' that people that are polite and have good manners (Wickham) must be good. Those that do not (Darcy) aren't. It takes her reading Darcy's letter twice (first time she dismisses it all as untrue), to realize that her perception of what is real and what isn't was very different. Not only must she use her feelings as a gauge but also 'think' about things. Then she's amazed at the discovery that she didn't even know herself well enough to figure things out.