Multitasking was never
actually simultaneous.

Context switching cost describes the gap between how fast and accurate someone is when they complete tasks separately versus when they interleave the same tasks by switching back and forth between them. That gap is measurable, not just a subjective sense of feeling scattered. Psychologists Joshua Rubinstein, David Meyer, and Jeffrey Evans studied it directly and found that shifting between tasks can consume as much as 40% of a person's productive time.

The term "multitasking" is somewhat misleading in this context, since true simultaneous processing of two complex tasks is largely a myth. What people experience as multitasking is almost always rapid task switching, and the brain pays a cost, however small, at every single switch. Individually, a switch might waste only a fraction of a second. Across a full day of frequent switching, that fraction compounds into a substantial share of lost time.

Switching tasks requires two distinct mental steps: disengaging from the rules and goals of the task you were doing, and engaging the rules and goals of the new one. Both steps take real processing time, even when the tasks are simple, and both happen before you can perform the new task at full accuracy and speed.

Complex or unfamiliar tasks cost more to switch into than simple, well-practiced ones. That's part of why switching from a focused work task to a quick app check, and then back again, can cost disproportionately more than the raw time spent on the app would suggest, both switches carry their own toll.

A single task switch is genuinely cheap in isolation, on the order of tenths of a second in controlled lab studies. The 40% figure doesn't come from any one switch being expensive. It comes from frequency: modern knowledge work involves dozens to hundreds of small switches a day, and each one, however brief, adds to a running total.

This is why the cost of context switching is so easy to underestimate in the moment. No single check ever feels like it cost 40% of anything. The toll only becomes visible at the level of a full day or week, which is exactly the scale most people don't naturally track.

A phone sitting within reach is available for a switch at essentially zero setup cost, no separate device to open, no application to launch, just a glance and a tap. That low barrier is precisely what drives switching frequency up, and frequency, not the size of any individual switch, is what turns context switching cost from a minor inefficiency into a meaningful share of the workday.

Removing notifications reduces one trigger for switching, but doesn't address the switches initiated by habit, boredom, or a passing thought, all of which happen without any external prompt at all.

Most advice for reducing context switching cost focuses on batching similar tasks and protecting blocks of uninterrupted time, both genuinely effective, and both still vulnerable to a phone offering an easy switch at any moment.

Fella keeps selected apps blocked by default, so the easiest, lowest-effort switch, a reflexive phone check, isn't available to begin with. one 5-minute emergency unlock per session covers a genuine need, and the block returns automatically when the window ends.