Work without edges David Allen, Getting Things Done (Penguin, 2001; rev. 2015), chapter 1. The term “knowledge work” comes from Peter Drucker.

Working memory George Miller’s famous paper put the capacity of short-term memory at “seven, plus or minus two” (Miller, “The Magical Number Seven, Plus or Minus Two,” Psychological Review, 1956). Later research showed that number included mental tricks like chunking; the modern consensus puts true working memory capacity at closer to four items (Cowan, “The Magical Number 4 in Short-Term Memory,” Behavioral and Brain Sciences, 2001).

Decision fatigue and heuristic reliance The pattern was described by Roy Baumeister and colleagues (“Ego Depletion: Is the Active Self a Limited Resource?”, Journal of Personality and Social Psychology, 1998). The study of Israeli parole judges, whose favorable rulings declined over each session and rebounded after breaks (Danziger, Levav & Avnaim-Pesso, “Extraneous Factors in Judicial Decisions,” PNAS, 2011); the same study is often read as showing a shift toward the “safe” status quo option under depletion. Similar end-of-session shifts toward low-effort shortcuts have been reported among physicians and financial analysts. Fair warning for the skeptics: both the underlying theory and the judges study have been challenged, the effect may be smaller than first reported, and at least one large healthcare study found no effect (see Glöckner, Judgment and Decision Making, 2016). I cite them for the everyday pattern they illustrate, which you can verify against your own late afternoons.

Unfinished tasks Bluma Zeigarnik, “Das Behalten erledigter und unerledigter Handlungen” (“On Finished and Unfinished Tasks”), Psychologische Forschung, 1927. For a modern take, unfinished tasks at week’s end have been linked to weekend rumination and worse sleep (Syrek et al., Journal of Occupational Health Psychology, 2017).

Memory and offloading (the “saving-enhanced memory effect”) Saving or writing information down frees cognitive resources and improves memory for what comes next, but only when the save is trusted (Storm & Stone, “Saving-Enhanced Memory: The Benefits of Saving on the Learning and Remembering of New Information,” Psychological Science, 2015). Relatedly, when we expect information to stay accessible, we remember where it lives rather than the thing itself, the so-called Google effect (Sparrow, Liu & Wegner, “Google Effects on Memory,” Science, 2011). Together these explain why the tasks you don’t capture stay more active in your mind than the ones you do.