The addict's reliance on the drug to reawaken her dulled feelings is no adolescent caprice. The dullness is itself a consequence of an emotional malfunction not of her making: the internal shutdown of vulnerability. From the latin word vulnerare, 'to wound', vulnerability is our susceptibility to be wounded. This fragility is part of our nature and cannot be escaped. The best the brain can do is to shut down conscious awareness of it when pain becomes so vast or unbearable that it threatens to overwhelm our capacity to function. The automatic repression of painful emotions is a helpless child's prime defence mechanism and can enable the child to endure trauma that would otherwise be catastrophic. The unfortunate consequence is a wholesale dulling of emotional awareness. 'Everybody knows there is no fineness or accuracy of suppression,' wrote the American novelist Saul Bellow in The Adventures of Augie March; 'if you hold down one thing you hold down the adjoining.' Intuitively we all know that it's better to feel than not to feel. Beyond their energizing subjective change, emotions have crucial survival value. They orient us, interpret the world for us and offer us vital information. They tell us what is dangerous and what is benign, what threatens our existence and what will nurture our growth. Imagine how disabled we would be if we could not see or hear or taste or sense heat or cold or physical pain. Emotional shutdown is similar. Our emotions are an indispensable part of our sensory apparatus and an essential part of who we are. They make life worthwhile, exciting, challenging, beautiful and meaningful. When we flee our vulnerability, we lose our full capacity for feeling emotion. We may even become emotional amnesiacs, not remembering ever having felt truly elated or truly sad. A nagging void opens, and we experience it as alienation, as profound as ennui, as the sense of deficient emptiness...