Why do men tend to keep love letters in files along with their other correspondence, whereas women keep them with their clothes? And if a letter is written but not posted, at whom is it really directed? As psychoanalyst Darian Leader shows, such questions go to the heart of sexual desire, which is never addressed to our flesh and blood companion, but always to something beyond him or her. In an engaging, at times startling, enquiry into the fundamental loneliness of each sex, Leader asks why relationships frequently run aground on the trivial question, ‘What are you thinking?’ If a man chooses as his partner a woman unlike his mother, why does he try to make her behave towards him exactly as his mother did, when he was a boy? And why might a woman decide not to spend the night with a man, after one glimpse of his apartment?