Many aspects of human sexuality are very puzzling, take celibacy as an example. This can be a choice in life, or a condition imposed by environmental factors. While attending a Marriage Encounter Weekend, Dave and Sally listened to the instructor declare 'It is essential that husbands and wives know the things that are important to each other.' He addressed the men. 'Can you each name and describe your wife's favourite flower?' Dave leaned over, touched Sally's arm gently and whispered, 'Self-raising, isn't it?' Thus began Dave's life of celibacy.