The last issue was about getting your estimates honest. This one is about protecting the corrected calendar once you have it, because an accurate estimate sitting in a fragmented day gets eaten by the same forces that made the old estimate wrong in the first place.
The Cost Is the Switch, Not the Interruption
A 4-hour block interrupted 6 times isn’t a 4-hour block with 6 small taxes on it. Researchers Joshua Rubinstein, David Meyer, and Jeffrey Evans measured this directly.1 Even simple, well-practiced tasks carry a measurable time cost when attention switches between them, a cost that exists independent of how hard either task actually is.
This is the mechanical reason a calendar chopped into 6 40-minute pieces produces less real output than the same 4 hours left whole. The math is simple arithmetic, not willpower or focus in the abstract: fewer switches, less tax.
This Week: Isolate
Pick one block on your calendar this week, at minimum 2 hours, and treat its edges as load-bearing walls. No meetings scheduled inside it, no messages checked during it, no “just this one thing” exceptions negotiated once it starts. The wall only works if it’s actually a wall.
The Porous Block
2 hours on the calendar, 6 small interruptions inside it. Every one felt reasonable in the moment, and the block never actually happened as planned.
Real output: a fraction of 2 hours
The Fortified Block
The same 2 hours, genuinely closed. Nothing gets in, including your own instinct to check something quickly.
Real output: close to 2 full hours
The wall exists so the 2 hours you carved out actually survive contact with the rest of your day.
"The successful warrior is the average man, with laser-like focus."
- Bruce Lee