What did you say of me that I did not deserve? For, though your accusations were ill-founded, formed on mistaken premises, my behaviour to you at the time had merited the severest reproof. It was unpardonable. I cannot think of it without abhorrence…I cannot be so easily reconciled to myself. The recollection of what I then said, of my conduct, my manners, my expressions during the whole of it, is now, and has been many months, inexpressibly painful to me. Your reproof, so well applied, I shall never forget: "Had you behaved in a more gentlemanlike manner." Those were your words. You know not, you can scarcely conceive, how they have tortured me; – though it was some time, I confess, before I was reasonable enough to allow their justice.

– Jane Austen

Pride and Prejudice, Chapter 58. Darcy reveals to Elizabeth that her refusal of his first proposal helped to open his eyes. He accepts that he behaved in an ungentlemanly fashion and his unpardonable behavior deserved her strongest reproof. His character has changed and developed as a result of Elizabeth’s rebuke of his manners and conduct. He has learned a great deal about himself and is brave enough to admit his fault.