Why Your Brain Needs Waves, Not Straight Lines
Your brain is not especially good at eight-hour focus marathons. Attention tends to rise, dip, and recover, even when your calendar pretends otherwise.
In the 1950s, sleep researcher Nathaniel Kleitman proposed an idea productivity culture still underuses: the brain moves through roughly 90-120 minute cycles of alertness and fatigue during sleep and, he argued, across the waking day. He called it the Basic Rest-Activity Cycle, or BRAC. The practical takeaway is not that every person needs a perfect 90-minute timer. It is that sustained effort needs recovery built in, because focus cannot keep doing the same job indefinitely without help.
Kleitman’s rhythm starts with a more alert phase, where complex thinking usually feels easier, then moves into a lower phase, where you may feel dreamy, distracted, or ready for a break. The exact timing varies by person, but the pattern matches something many people already notice: there are windows when the work opens, and there are windows when pushing harder mostly makes the work thinner.
This also fits what researchers have observed in some high performers. Anders Ericsson's deliberate-practice work, later popularized as the "10,000-hour rule," found that the best violinists practiced in focused sessions of about 90 minutes, then rested. They were not simply grinding for hours without pause. Their practice had edges, and the recovery around those edges helped the next session matter.
When you push through a fatigue dip by answering more email, forcing focus, or caffeinating through the fog, you can end up leaning on your body's stress response. Planning gets harder, anxiety can rise, and the work often becomes more brittle even though you are still technically at your desk. That is one reason a workday can feel exhausting even when little obvious progress happened. Some of the effort went into overriding rest signals instead of using them.
The gentler approach is to treat deep work as a block with a natural ending. Try a focused stretch, stop before the work gets ragged, and give the low point something useful to do: a walk, light movement, a little daydreaming, or low-cognitive admin that does not pretend to be deep work. After a few days, you can usually tell whether your own window is closer to 75 minutes or two hours, and that information is more useful than copying someone else’s schedule.
Traditional goal tracking often assumes linear effort, where more hours simply means more progress, but attention is messier than that. A focused block often beats four scattered hours, and rest can be part of progress rather than a guilty interruption from it. The useful reframe is that your energy is less like a straight line to manage and more like a wave to plan around.
How Annet applies this
Annet’s wave states are meant to make oscillation feel normal rather than alarming. Building, Resonating, and Fading describe movement over time, so a low-energy period can be treated as information about the goal’s rhythm instead of proof that the goal is failing.
Health Score tracks momentum alongside completion, which means a minimum viable check-in can still keep a goal connected during a trough. The Zen Guide persona reinforces that same idea by helping you meet fatigue with curiosity instead of judgment.
References
- Kleitman, N. (1982). Basic rest-activity cycle - 22 years later. Sleep, 5(4), 311-317.
- Lavie, P., & Scherson, A. (1981). Ultrashort sleep-waking schedule. I. Evidence of ultradian rhythmicity in 'sleepability'. Electroencephalography and Clinical Neurophysiology, 52(2), 163-174.
- Ericsson, K. A., Krampe, R. T., & Tesch-Römer, C. (1993). The role of deliberate practice in the acquisition of expert performance. Psychological Review, 100(3), 363-406.
- Rossi, E. L., & Nimmons, D. (1991). The 20-minute break: Reduce stress, maximize performance, and improve health and emotional well-being using the new science of ultradian rhythms. Tarcher.
