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Explain xkcd: It's 'cause you're dumb.
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Once Per Day
I'm not totally locked into my routine—twice a year, I take a break to change the batteries in my smoke detectors.
Title text: I'm not totally locked into my routine—twice a year, I take a break to change the batteries in my smoke detectors.


Ambox notice.png This explanation may be incomplete or incorrect: Links should be explained by one or two sentences.

Many news reports on health recommend the "best" way to perform the processes, such as eating, drinking, exercising, or sleeping, that are required to live healthy. These reports tend to give such factors as a type of food to consume regularly, the amount of a nutrient to consume, or how long to exercise, in terms of what or how much to do daily. A simple example of this is the proverb, "An apple a day keeps the doctor away." Perhaps this kind of advice is overthinking things, but Cueball decides to follow it strictly as explained in the caption.

So when Megan asks Cueball what his plans are, he just lists his routine consisting only of things that the news has told him exactly how often to do.

His list includes the following, which he has to do once per day:

Two obvious problems arise with these "you should do ... daily" tips. They are often based on population studies, but they may be harmful in the case of some individual persons. This health-related advice would be beneficial in, say, 60 or 70% of the population, but may be ineffective in other 20% of the people, and deleterious in 10%. This especially relates to the suggested daily intake of aspirin.

The second problem is the (more or less) scientific foundation of this advice. For example, you study the effects of a daily glass of red wine. But there is certainly no study that has ever observed the interaction of these ten specific health advices. For example, tannins (which occur in red wine and coffee) are known to absorb certain substances, which may influence the way apples and eggs are digested.

Of course, if Cueball only does these things, then he can't/doesn't attend to other important matters, such as going to work, which most likely allows him to buy the recommended materials in the first place. And the routine is subject to change as soon as he hears another such daily recommendation on the news (which won't happen, though, because he hasn't heard a recommendation to tune in to the news every day - so, poor Cueball is trapped in his daily schedule).

In the title text Cueball explains that his daily routine is not completely fixed. It is broken twice a year, since he also follows public information campaigns suggesting the replacement smoke detector batteries twice a year. While the US National Fire Protection Association recommends a replacement at least once per year others suggest every time when the clock changes according to daylight saving time, i.e. twice a year. (All such recommendations will likely become irrelevant as citizens of the United States, starting in California, are encouraged to replace their existing smoke detectors with new models containing irremovable ten-year batteries.) This is just another example for official overdone recommendations nobody follows, in this case since smoke detectors make annoying beeps when their batteries run low and thus rarely need routine replacements before then.


[Megan and Cueball are standing together, facing each other.]
Megan: Got any plans for the day?
Cueball: I'm going to eat an apple, an egg, one baby aspirin, and a piece of dark chocolate, drink six glasses of water, one glass of red wine, a cup of coffee, and a cup of tea, then do 30 minutes of exercise.
Cueball: Then back to sleep for another 8 hours!
[Caption below the panel:]
I only do things that news stories have specifically told me to do once per day.


  • Fire alarms were also the subject at 1794: Fire.
  • Drinking six glasses of water per day has been the subject in 1708: Dehydration, and earlier, when it was more common to say eight glasses per day, in 715: Numbers.

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