The focusing question and the domino effect
Gary Keller's entire method fits into a single question: "What's the ONE thing I can do such that by doing it everything else will be easier or unnecessary?". This focusing question forces you to prioritize: among all your tasks, only one truly matters right now.
The authors illustrate the principle with the domino effect: a domino can knock over another domino 50% larger than itself. Lining up dominoes of increasing size, the 57th would nearly reach the distance from the Earth to the Moon.
Each well-chosen win thus triggers a chain reaction. Ask yourself the question every morning, before you even open your email, and let it guide your day.
Start each day by identifying THE task that makes everything else easier or unnecessary.
Time blocking: protect your priority
Identifying your priority is not enough: you have to reserve time for it. Keller and Papasan recommend blocking four hours every morning in your calendar to work exclusively on your ONE Thing, before any other demand.
Treat this time block as an unbreakable appointment: door closed, notifications off, a ready-made answer for outside requests. Because protecting your priority means saying no, or at least "not now", to almost everything else.
As the authors remind you: every "yes" granted to other people's requests is a silent "no" addressed to your own goal.
Reserve an untouchable time block every day for your priority, and learn to say no to the rest.
The myth of multitasking
Multitasking is an illusion: your brain does not do two things at once, it switches from one task to another, paying a refocusing cost every time. Trying to juggle everything means doing everything worse and slower.
The solution is not willpower, which the authors describe as a depletable resource, much like a battery. It is habit. They cite a study from University College London: it takes 66 days on average for a behavior to become automatic.
So focus your discipline on one habit at a time, until it no longer requires effort, then move on to the next.
Give up multitasking: install one habit at a time, for about 66 days.
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