From Sears and Sears’ parenting book “The Baby Book: Everything You Need to Know About Your Baby From Birth to Age Two“:

Mark and Kelly were first-time parents who were blessed with a high-need baby—especially at night. They were sensitive and responsive parents, but one day a friend gave them a cry-it-out book, with the admonition, “Now you’ll be tempted to give in, but harden your hearts and in a few nights he’ll sleep.” As their one-year-old baby screamed, these sensitive parents stood sweating and hurting outside his door, afraid to go in and “break the rules.” Each night baby’s night waking decreased, as did the parents’ attachment. Baby cried in a feeling of mistrust and cried the sensitivity right out of the parents. Previously Mark and Kelly had taken baby Matthew with them everywhere because they wanted to and it felt wrong to leave him. Well, it was now easier to leave him. Getaway weekends extended to getaway weeks. A distance developed between parents and baby. More was cried out of the family than only night waking.