The 90-Minute Rule
Your brain cycles through 90-minute focus periods, then demands rest. Fighting this costs energy. Working with it is free leverage.
Your brain runs on 90-minute cycles. Not because of some productivity hack, but because of basic physiology.
Sleep researcher Nathaniel Kleitman discovered that the same ultradian rhythms governing REM sleep continue during waking hours. Every 90-120 minutes, your brain moves from high alertness to a dip that demands rest. Fight it and you burn willpower. Work with it and you get natural recovery built in.
The application is simple: structure your day in 90-minute blocks of focused work followed by 15-20 minutes of real rest. Not email. Not Slack. Actual mental disengagement.
The hack: Block your calendar into 90-minute focus sessions. Set a timer. When it ends, stop. Walk away from your desk. The break isn't a reward for finishing. It's part of the work.
You don't need more discipline. You need to stop fighting your biology.
