The concept of using a 28 or 30 day period dedicated to a purpose has a long history in humanity. A month of mourning is used in some cultures to reflect on the loss of a loved one. Many religions feature a month of prayer and fasting as a way of focusing on one's faith. In more mundane applications, the 30 day "trial period" for shareware has long been the standard. It provides a long enough time to really experience the purpose while still providing a defined end.
Shorter commitments frequently don't really give you the same depth that a longer experience can. To me, this is similar to how a 90 minute movie compares to the longer form storytelling like the Sopranos. I certainly wouldn't want all of my TV/Movies to follow a 60 hour story arc, but on occasion, it provides an interesting experience.
The recent success of the film "SuperSize Me" and Mr. Spurlock's new TV series, "30 Days" have drawn attention to using the 30 Day Challenge/Experiment to get a better understanding of something, challenge yourself to some improvement, learn a new skill or otherwise gain a better understanding of yourself and your surroundings. They've explored minimum wage/unskilled work and the problems with it, living with the stigma of being a Muslim in America, living off the grid, etc.
Steve Pavlina explained his take on this back in April, relating the 30 Day Challenges he's undertaken, many to deal with food. Personally, I'm in the middle of a 30 Day Challenge to get up at 5:30 every morning, 7 days a week. Coming in November, I'm taking on the 30 Day Challenge to write a novel in a month.
The challenge also needs to be specific and focused as you mentioned. One of the reasons that New Year's resolutions fail is that people are very vague when stating them. When you make them vague, they're open to "negotiating" later. For instance, if I had decided to "get up early" instead of "before 5:30 am, 7 days a week", I can try to negotiate with myself on the first morning about what "early" means. Then, on Saturday, I can renegotiate saying that I didn't mean weekends. Soon thereafter, the whole thing falls apart.
When creating goals of any kind, but 30 Day Challenges specifically, answering any questions you may ask yourself later at the beginning will improve the odds of completing it.
In your teeth brushing example, the questions I'd ask myself before commiting to it would be: what about restaurants, friends' homes, on vacation, somewhere without a toothbrush (do I go buy one?), etc. By answering these questions at a point where you ARE exhibiting the willpower you get them out of the way before you start getting weak.
That's actually a part of most of the religious fasts as well as the 30 Days TV show. The rules (are bread and water OK?, etc.) give you a structure to lean against when it gets hard. You effectively have someone or something to blame when arguing with yourself, "I know you want that donut, but donuts aren't allowed on the program." "I know it would feel good to hit the snooze bar and sleep for 10 minutes, but that would put us at 5:40 and the rules say 5:30am."
Incidentally, this is why structured diet programs tend to work longer than just "eating better".
What 30 Day Challenges are you interested in taking on? What do you hope to learn? To change? To accomplish?
