They say if you do something for 21 days straight, it becomes a habit.
Just a counter-hypothesis: Anyone who gets away from the routine for more than 3 days, starts to get bored and distracted.
If you are away from your home and you’re not on a vacation, after 3 days you might get homesick.
If you’re preparing for an exam or watching a tv show or reading a book and if you aren’t hooked after 3 chapters, 3 episodes, or 3 pages, you lose the interest.
If you are in a hospital for more than 3 days, you start getting bored. Moreover, people who were visiting you might slowly become less frequent.
Just a counter hypothesis to the 21 day rule.