Attention degrades over the course of the day. The quality of focused cognitive work you can do at 9 AM is not equal to the quality at 4 PM — not because you've become less intelligent, but because attention is metabolically expensive and the supply depletes with use. Decision fatigue is a related phenomenon: the quality of decisions made late in the day degrades, which is why judges give less favorable rulings before lunch and why you should not review contracts at 5 PM on a Friday.

This has practical consequences for how you structure work. The hardest problem, the one requiring the most sustained focus, should go in the best hours. The best hours are probably morning, before the inbox and the meetings have consumed the available supply. Administrative tasks, email, the work that requires coordination rather than concentration — these can go in the depleted hours without much loss.

The open-plan office, the always-on messaging culture, the meeting that could have been an email — these are designs that consume the attention supply without discrimination between the expensive hours and the cheap ones. They're resource allocation failures, treating all hours as equal when the resource distribution is highly unequal.

Know your depletion curve. Allocate accordingly. The expensive work deserves the expensive hours.— Jen the Dev, from the void.