This happens because babies are born with several reflexes—including suckling—that help them survive before they develop voluntary skills of their own.
Suckling is also incredibly comforting for your baby. When your little one suckles on your breast the hormone cholecystokinin (CCK) is released, creating a sleepy feeling. This is why some babies love to nurse for comfort and a soother can help calm your little one—even if it’s not a long-term strategy. Soothers do often help, but mum is number one!