You don't lose a minute.
You lose 23.

Holding a codebase's mental model in your head is fragile in a specific way most other work isn't. Research on developer flow states puts the cost of a broken concentration at up to 23 minutes to fully reclaim, and the interruptions themselves arrive every 3 to 10 minutes on average. A GitHub-cited study estimates that frequent disruptions from meetings, messages, and quick questions can erase up to 82% of a developer's productive time.

The most common flow breakers aren't meetings, they're notifications: Slack, email, calendar alerts. And the damage doesn't require a response. Just seeing a notification appear on screen can be enough to break concentration, even if you don't touch it. Context switching more broadly has been shown to cost roughly 40% of a person's productive time across a workday.

Most knowledge work tolerates some fragmentation. Writing an email, reviewing a document, these can survive a five-minute gap without much cost. Programming is different because the "state" you're holding isn't written down anywhere, it's a live mental model of variable states, call stacks, and the specific bug or feature you're mid-reasoning on. An interruption doesn't pause that model, it erases it, and rebuilding it is where the 23 minutes goes.

This is why "I'll just check it real quick" is a worse trade for a developer than for almost any other role. The quick check itself might take ten seconds. The mental model it costs takes 23 minutes to rebuild, if it gets rebuilt at all before the next interruption arrives.

A lot of engineering teams have gotten reasonably good at managing Slack noise, notification schedules, batched standups, one meeting a day instead of three. Research on meeting frequency backs that instinct: teams holding one meeting a day maintain progress on daily goals nearly 99% of the time, a number that drops to 14% once a third meeting gets added.

None of that Slack discipline touches the phone sitting next to the keyboard. A text, a social notification, a game update, these interrupt the same fragile mental model Slack does, but they usually aren't part of any team's focus-time policy because they're personal, not professional.

iOS Focus modes can silence notifications during a coding block, but the apps are still one tap away, and silencing a notification doesn't stop the reflexive check that happens anyway. The habit of glancing at the phone between compiles or while waiting on a test suite doesn't require a notification to trigger it.

Fella blocks selected apps at the iPhone level using Apple's Screen Time framework, so there's nothing to open even during the in-between moments. One 5-minute emergency unlock a day covers a genuine need, and work tools like Slack, email, and ticketing apps can stay unblocked the whole time.

1. Block the apps that aren't part of the job. Social media, games, and entertainment apps, leave Slack, email, and your ticketing system unblocked.

2. Let the block hold through the whole coding day. No toggle to switch off between tickets.

3. Use the emergency unlock for something real. One 5-minute window a day, not a compile-time scroll.

4. The apps lock again automatically. No willpower needed while you're mid-stack-trace at 4pm.