"In addition to knowledge, there is another force that operates in friendship and intimate relationships and that is the element of mystery. No matter how much we strive to know those whom we love, we can never fully plumb the depths of their innermost being, for, at our core, each of us is an unfathomable mystery. Just as Ein Sof is unknowable, every being, made in the divine image, is an infinite and inscrutable mystery. Not only are we mysteries to one another, but we are largely mysteries to ourselves, and love is one of the primary ways we begin to discover who we are and who we might become. Relationships provide us with a mirror in which we can see ourselves more clearly.

"While all relationships are shaped by the dialectic of knowledge and mystery, the interplay of these two forces has special significance in romantic love. At the same time that we yearn to experience the safety and security that comes with intimate knowledge of our partner, in order to feel erotic desire we also need to experience our partner's mysterious otherness. Eros flourishes where there is room for imagination and fantasy. It requires a gap over which the spark of desire can leap, as the couple therapist Esther Perel writes: 'Eroticism thrives in the space between the self and the other. . . . To sustain an elan toward the other, there must be a synapse to cross.'

"Humans share these two fundamental needs: We need to feel a sense of safety and security in our lives — to have a home in the world where we are known and feel accepted for who we are. But we also have a need for adventure, for the novelty and surprise we experience when we go forth on a journey. While our need for safety and security leads us to seek permanence and dependability in our intimate relationships, our need for novelty and adventure leads us to enter unknown and uncertain spaces. In a sense we are walking contradictions. At the same time that we yearn for emotional intimacy and closeness, we also need space in order to fulfill our erotic desires. This is why eros is strongest during the early stages of romantic love, when unknowns outweigh the known, and can fade as lovers become overly familiar."