They both lost someone close to them, and that loss affected the character they became. Both have a strong fear of oppression; Carissa is influenced by her lifestyle and past, while Septimus fears the entire world. Many wonder why Wool didn't use Septimus as Clarissa's male counterpart, however that would have brought the characters too close. When they are separated, their problems and fears stand on their own. If they were to be reunited it would completely change the dynamic of the novel. Furthermore, by keeping them separate, Woolf creates a metaphor for how people can be so caught up in their own thoughts that they don't even notice who's around them and what's wrong.