Demarketing requires discipline: the discipline to decide what you’re not going to do, and then the discipline to stick with the decision.  Some people have this kind of discipline in spades:

Xiang Yu was a Chinese general in the third century B.C. who took his troops across the Yangtze River into enemy territory and performed an experiment in decision making. He crushed his troops’ cooking pots and burned their ships.
He explained this was to focus them on moving forward — a motivational speech that was not appreciated by many of the soldiers watching their retreat option go up in flames. But General Xiang Yu would be vindicated, both on the battlefield and in the annals of social science research.

In The Advantages of Closing a Few Doors (New York Times February 26, 2008), John Tierney discusses the work of MIT behavioral economist Dan Ariely.  As Tierney describes, Ariely proves scientifically that brainpower is not a sufficient driver for discipline:

Most people can’t make such a painful choice, not even the students at a bastion of rationality like the Massachusetts Institute of Technology, where Dr. Ariely is a professor of behavioral economics. In a series of experiments, hundreds of students could not bear to let their options vanish, even though it was obviously a dumb strategy (and they weren’t even asked to burn anything).

The experiments involved a game that eliminated the excuses we usually have for refusing to let go. In the real world, we can always tell ourselves that it’s good to keep options open.

…Your child is exhausted from after-school soccer, ballet and Chinese lessons, but you won’t let her drop the piano lessons. They could come in handy! And who knows? Maybe they will.

In the M.I.T. experiments, the students should have known better…

But they didn’t act like they did.  Read the article and learn about the psychology.  Then remind yourself that discipline is hard, and prepare yourself for the effort.

A Toyota Motor Corp employee died of overwork after logging more than 106 hours of overtime in a month, a judge ruled Friday, reversing a ministry’s earlier decision not to pay compensation to his widow. …The employee, who was working at a Toyota factory in central Japan, died of irregular heartbeat in February 2002 after passing out in the factory around 4 a.m.Overworking is a serious issue in Japan, where an average worker uses less than 50 percent of paid holidays, according to government data.

In fiscal year 2005-2006, the labor ministry received 315 requests for compensation from the bereaved families of workers who died of strokes and other illnesses seen as work-related.

– Kubota and Kim, Court Rules Employee Worked to Death, Reuters News Agency, 30 November 2007

The first case of karoshi was reported in 1969 with the death from a stroke of a 29- year old, married male worker in the shipping department of Japan’s largest newspaper company [1]. Karoshi can be translated quite literally as “death from overwork.” The major medical causes of karoshi-deaths are heart attack and stroke, including subarachnoidal hemorrhage (18.4%), cerebral hemorrhage (17.2%), cerebral thrombosis or infarction (6.8%), myocardial infarction (9.8%), heart failure (18.7%), and other causes (29.1%) [2]. The Ministry of Labor began to publish the statistics on karoshi in 1987, as public concern increased [3]:

Nishiyama and Johnson: Karoshi-Death from overwork: Occupational health consequences of the Japanese production management (Sixth Draft for International Journal of Health Services). 4 February 1997.

By comparison:

GENEVA (ILO News) - US workers put in the longest hours on the job in industrialized nations, clocking up nearly 2,000 hours per capita in 1997, the equivalent of almost two working weeks more than their counterparts in Japan where annual hours worked have been gradually declining since 1980, according to a new statistical study * of global labour trends published by the International Labour Office (ILO).

– International Labour Organization press release “Americans work longest hours among industrialized countries, Japanese second longest. Europeans work less Time, but register faster productivity gains New ILO statistical volume highlights labour trends worldwide”, 6 September 1999.