[...] In the face of the helplessness and vulnerability we feel at such moments, infidelity can be an act of defiance. Freud described eros as the life instinct, doing battle with thanatos, the death instinct.

Those same people may have previously felt tempted, but I wonder if it is the brusque confrontation with the brevity of life and its fragility that emboldens them to seize the day and act. Suddenly they are unwilling to settle for a life half-lived. “Is this all there is?” They hunger for more. Compromises that seemed reasonable yesterday become unbearable today. “Life is short, have an affair.” AshleyMadison.com’s infamous slogan may seem crude, but it is aptly targeted. Stories like this are so common that I now routinely ask my patients: “Have you suffered any losses, deaths, or tragedies in the past few years?”

Maybe it is death with a capital D, or maybe it is just the deadness that creeps up from dulling habit—whatever the case, I now see these affairs as a powerful antidote. “Love and Eros wake up the most tired person,”1 writes Italian sociologist Francesco Alberoni. The thirst for life triggered in such an encounter topples us with an irresistible force. It is often neither planned nor sought. The unexpected boost of erotic desire galvanizes us beyond the mundane, abruptly breaking the rhythm and the routine of the quotidian. Time slows down. The inexorable advance of age seems to lose its momentum. Familiar places take on fresh beauty. New places beckon to our reawakened curiosity. People report that every sense feels amplified—food tastes better, music never sounded so sweet, colors are more vivid.