The Ferber method or the Cry-it-out method of solving infant sleep problems can actually be traced back to the 19th century book The Care and Feeding of Children by Dr. Emmett Holt. Though Dr. Richard Ferber’s method is not just about leaving a baby to cry it out, it is aimed at letting a baby learn to self soothe, but there are many arguments against Ferberization or Ferbering.
What the Ferber method entails: Ferbering requires that night time rituals be established and followed, which is a good idea. It then requires the parent to leave the baby in bed and leave the room. 
Comforting the baby must be done without picking up the baby and intervals before coming in to comfort must be lengthened until baby learns to sleep by themselves.
This training in sleep is to start for infants as early as three months of age.
This can be very traumatic for the parents: Ferbering requires you to let the baby cry for 5 minutes before offering comfort the first day, then increase that 5 minutes to 10 the second day, to 15 the third day and so on progressively increase the time. So basically parents have to be able to listen to their baby cry inconsolably for long periods until he or she sleeps out of exhaustion.
This is hard on the parents, and because babies cannot speak we don’t know how hard it is for them. And there certainly are kinder and gentler ways of getting kids to sleep.
Research has shown that babies do better if they are held when they cry: There are studies that have shown that the cry it out method, can cause permanent brain changes in a baby and can lead to health issues later in life; even anxiety disorders, including panic attacks.
Long bouts of crying also cause congestion which may lead to an ear infection in cases. In many traditional cultures where co-sleeping is the norm, this would amount to cruel neglect of small infants and even in the West, “No cry” advocates think Ferbering is harmful to children, and that it could undermine a child’s sense of security in the world.
Dr Ferber has himself admitted that his advice required modifications: In the 2006 edition of his book Solve Your Child’s Sleep Problems Dr Ferber made certain modifications that were an implied acceptance that some of this previous advice may not have been very sound.
In this subsequent edition of his book he has shown himself more open to the idea of co-sleeping and says that parents should do whatever they are comfortable with.
