They recommend the cry it out sleep training which is proven to cause psychological problems for your baby! it works because it shocks them so much that their amígdala shuts down after so much stress because they can't take that much cortisol. Imagine what all that stress does to your baby! Baby will perceive a lack of care from your part. It's the worts thing you can do long term, please do your own research before attempting this. It's really cruel method and should be forbidden to use.