Time is the only resource you cannot manufacture, buy, or recover. Every hour spent on one activity is an hour permanently diverted from every other possible activity. This makes opportunity cost the central concept in time economics.
After about 4-5 hours of genuine deep work, cognitive performance declines measurably. Pushing beyond this point feels productive but the marginal output per hour drops sharply. Schedule demanding work first and administrative tasks for lower-energy windows.
A project you have invested 50 hours in should not automatically receive 50 more simply because of prior investment. The question is always: given where I am now, is this the best use of my next hour?
Time management is about allocating finite hours to their highest-value uses. Economic concepts like opportunity cost, marginal returns, and comparative advantage provide a rigorous framework for these decisions. The goal is maximum value, not maximum busyness.