Marianne first learns to show emotional restraint. She comes to realize that she doesn't need to always wear her heart on her sleeve. She learns to restrain herself from jumping to conclusions. At the beginning of the novel, she rushes headlong and impulsively into love with the romantic Willoughby and simply assumes that since he seems to share her feelings, they will be engaged and then married. Leading so much with her emotions and her heart hurls her toward destruction. When she find outs that Willoughby, for pragmatic financial reasons, is going to marry another woman, the shock makes Marianne so ill that she almost dies. She is far too emotional and must learn to restrain her feelings and use more sense, like her sister.
Second, Marianne learns not to judge a book by its cover. At first, she rejects the 30-something Colonel Brandon as much too old for her. Later, sobered by her experiences with Willoughby, she comes to realize there is much worth beneath Brandon's "elderly" surface. Willoughby might have been more dashing, handsome, and romantic, but Brandon has the steady character and devoted heart that she needs. His inner worth becomes apparent to her.