It's about motivation, and the fact that it's really hard to get (or stay) excited about something when you don't have tangible results for your efforts. Martha Beck,PhD seems to think that 4 days is the magic amount of time needed to start successfully on a weight loss plan. She says it's not so long (like a week) that it's too hard to stick to it, but it's just long enough to start seeing the results of your labors -- which will in turn inspire the motivation needed to continue.

I haven't read her book on this subject, The Four Day Win, but in reading what she has to say about the basic principles it makes perfect sense. Some of it is based on setting realistic and specific goals, planning out rewards, and even writing out and signing a contract. These are all things I've heard of before, and throwing in a "baby steps" idea sounds like a good plan to me.