Ever wonder about the ubiquity of offers to try out a service for free for 30 days? Why does the local gym not offer two weeks' free membership?
The question bears particular relevance at a time when Americans, by long tradition, make New Year's resolutions.
I believe the answer lies in a behavioral economic insight that savvy marketers employ to overcome resistance to the adoption of their products—namely, that when you've adopted a behavior for a period of 30 days, you have a greater likelihood of continuing that behavior.
Marketers have plenty of tricks up their sleeves. Why, for example, is a free sample workout not sufficient to keep you a member of a gym?
The free sample—say, for a cup of coffee or a chocolate—may be based on the principle of reciprocity or may be intended to break down resistance to trying something new or different from the customer's usual choices.
Those cases are distinguishable from the case of a gym because there, you are being asked to do something that is, essentially, painful. For that, you need a greater degree of encouragement.
I suspect that dieting is harder still than a new exercise regimen. One can start to appreciate the benefits of exercise within days, and one can get used to the pain within a month. But if you diet successfully in January but family birthdays in February or March put a greater than usual quantity of cake in front of you, you can blow all your progress quickly and get discouraged. For a diet, a person probably needs to maintain discipline throughout a calendar year, including Thanksgiving and Christmas dinners (or the latkes and jelly donuts that challenge Chanukah celebrants).
