What does it mean that the energy cost of context switching?

Every context switch depletes energy — batch similar tasks to conserve it.

Example: You sit down at 9:00 AM to write the product roadmap — your ONE thing (L-0685), placed in your peak window (L-0705). Fourteen minutes in, a Slack notification appears. You glance at it: a teammate asking about an API change. You switch tabs, read the thread, type a three-sentence reply. Ninety seconds of clock time. You return to the roadmap. But you are not returning to the same cognitive state. Your brain is still holding fragments of the API question — the schema migration, the breaking changes, the teammate's deadline. Sophie Leroy calls this attention residue: the cognitive traces of Task A that persist into Task B. You reread the last paragraph you wrote, trying to reconstruct where you were headed. Three minutes pass before the thread of thought reconnects. Five minutes after that, your phone buzzes — a calendar reminder for a 10:00 AM check-in you forgot to reschedule. You start thinking about the agenda. The roadmap recedes again. By 10:00, you have spent fifty-one minutes at your desk and produced twenty-two minutes of actual roadmap thinking. Twenty-nine minutes — 57 percent of your peak window so far — have been consumed not by the interruptions themselves but by the switching costs surrounding them.

Try this: Track your context switches for one full workday. Keep a running log — a notebook beside your keyboard or a simple text file — and every time you shift from one task, application, or cognitive mode to another, note three things: the time, what you switched from, and what you switched to. Do not try to reduce your switches today; just observe. At the end of the day, count the total number of switches. Then identify the three longest unbroken stretches of single-task work and the three most fragmented hours. For the fragmented hours, estimate how much time was lost to reorientation after each switch — the seconds or minutes spent trying to recall where you were. Finally, group your switches by type: planned transitions (finishing one thing and starting the next), interruptions (someone or something pulled you away), and self-interruptions (you pulled yourself away). Calculate the ratio. Most people discover that self-interruptions — checking email, opening social media, switching to an easier task — outnumber external interruptions by two to one.