You closed the spreadsheet an hour ago, yet while writing the report you keep rehearsing spreadsheet thoughts. You’re not distracted — you’re experiencing what psychologist Sophie Leroy named attention residue: part of your attention stays stuck on Task A long after you’ve moved to Task B. The thesis: busyness isn’t the enemy of focus; switching is — and the fix is structural, not motivational.

The residue experiments

Leroy’s 2009 paper “Why is it so hard to do my work?” forced task switches in the lab: some participants finished word puzzles before moving to hiring decisions, others were interrupted mid-puzzle. The interrupted group performed significantly worse on hiring — their minds kept processing the unfinished puzzles, consuming working memory that Task B needed. The mechanism is the Zeigarnik effect: the brain holds incomplete goals in an activated state, adaptively, until resolution. In a fragmented workday of twelve open loops, that adaptive feature becomes a permanent tax.

Cal Newport popularized the finding in Deep Work (Wharton summary), drawing the sharp conclusion: even “just checks” — twenty seconds in the inbox — leave residue disproportionate to their duration, because each glance usually reveals something you can’t act on, creating a fresh open loop. Checking email ten times a day doesn’t cost three minutes; it costs ten episodes of degraded cognition. As Newport’s arcade-game analogy (Study Hacks, 2016) puts it: every glance is a new target your attention must later detach from.

The structural fixes

Leroy’s second finding is the hopeful one: finishing Task A under time pressure sharply reduces residue — the deadline creates cognitive closure, confidence that the task is truly done. From this, practitioners derive a protocol (10000Hours synthesis): end each work block with a micro-resolution (finish the sentence, note the next action), batch all communication into one or two windows, protect long morning blocks for the hardest work, and pick tomorrow’s priority tonight so “what should I do?” doesn’t itself become residue.

Counterpoint: switching has its uses

Single-tasking fundamentalism overshoots. Incubation — background processing of a hard problem during a walk or a different task — is real and valuable; strategic switching between complete work blocks aids creativity. Some roles (support, management) legitimately run on responsiveness, where batching windows rather than monastic isolation is the honest adaptation. And for ADHD minds, hyperfocus creates a reverse pattern — inability to disengage — needing different tools entirely.

Takeaway

Tomorrow, try one change: a 90-minute morning block with the phone in another room, ending by writing down the next action before you switch. You’re not becoming more disciplined. You’re finally letting your attention arrive where you already are.