What is the most successful sleep training method?

If you look at the science, the science says, it's extinction. Put the baby in when it's awake. Leave the room. They'll cry, of course. Don't go in all night long. The problem with that, is well, sometimes it doesn't work. Most of the parents that I work with can't do it. It breaks their heart. And so they go in, and they start being inconsistent. And they cause more problems.