This section from Elinor in Ch 17 struck me:

"I have frequently detected myself in such kind of mistakes," said Elinor, "in a total misapprehension of character in some point or other: fancying people so much more gay or grave, or ingenious or stupid than they really are, and I can hardly tell why, or in what the deception originated. Sometimes one is guided by what they say of themselves, and very frequently by what other people say of them, without giving oneself time to deliberate and judge."