I don't believe in "methods" when it comes to babies. If mothers don't let "the world" butt in and tell them what they should be doing; all it takes to have a baby develop really well is to take good care of the baby, make him feel super-secure and loved by being responsive to him and by the way a mother holds and talks to her baby. Talking to him, singing to him, making him laugh, and making eye contact are all part of nurturing too.
When babies feel super-secure and loved, that lays the foundation (even at the "brain-chemical" level) for his developing well and being able to learn new things as he continues to develop. Brain connections are forming, and if parents miss that "boat" the child suffers for it.
When babies develop well they DO learn to self soothe eventually. My first-hand experience was with my own three kids. I've had a lot of other experience with babies and toddlers too, though. Most normal mothers have common sense and a maternal instinct. They should use both, instead of looking to outsiders with a book to sell, or a willingness to turn someone else's baby into an experiment, for parenting "methods". (Once children get past preschool age things can get a little trickier sometimes, but babies all pretty much "work" the same way.)