the PDD model was created due to robertson and robertsons research....where they observed a boy named john......go through these stages.......it had important implications because back in the day when mothers were preggers and they were about to drop (lol, sorry if that sounds blunt)........they would leave their kids in care homes.........however such research showed that it affected children's attachment......which was why they changed rules ...for e.g. now they allow children to have contact with their mothers.........