The correct answer given for this question is oversimplified in this controversial matter. I am concerned about leaving a six month old baby to cry for 2 hours a night. That seems extreme to me. Babies can’t speak to the doctor only parents can. It may be good for the parent’s sleep in the short term but I am concerned about the long term effects especially in some babies who may have vulnerabilities that are not yet identified. While in the USA and UK this type of sleep training may be more promoted, around the world and in the last hundred thousand years or so babies of that age have slept with their parents.