"A woman of seven-and-twenty," said Marianne, after pausing a moment, "can never hope to feel or inspire affection again..." --Sense and Sensibility
I'd forgotten what extremes Elinor and Marianne are, as if Jane Austen set out to create caricatures for her title. Their temperaments are so defined that I think it would be difficult to spend any time with them, which I've never felt about any other Austen characters. I do believe Marianne is the only person I've ever seen actually fall into the depths of despair. When Elinor enters Marianne's room after Willoughby's rejection letter has arrived, Marianne thrusts the packet in Elinor's hands, presses a handkerchief to her mouth, and "fairly scream[s] with grief." Once she falls in love with Willoughby, nothing else can entertain her; when he is absent she has interest in nothing; and after his rejection she cannot even see another person without falling into another paroxysm. Elinor is remarkably compassionate towards her; I'd be inclined to give her a good smack.
Compare these reactions to Elinor's state when she learns that Edward Ferrars has been secretly engaged to Lucy Steele the whole time he has been acquainted with the Dashwoods. She is, naturally, shocked at the news, but instead of retiring permanently to her bedroom, does her best to rationalize the situation and gain an understanding of what must have happened between the two young people. Of course she is unable to share the knowledge with anyone, since Lucy has entreated her to keep the affair secret, and yet it is difficult to imagine that anyone could be capable of fashioning such perfect composure. She can even bring herself to mention the matter again to Lucy, and discuss it calmly despite suspecting the other girl's jealousy.
Odious thinks that their temperaments build off each other: that Marianne increases her passion and emotional state because she thinks Elinor should express herself more; and Elinor retreats into her rational shell because she wishes Marianne would be more restrained. There is certainly some truth to this, but I still wouldn't enjoy an afternoon with them as much as I would with the Bennetts.