From The Effective Executive: The Definitive Guide to Getting the Right Things Done
The output limits of any process are set by the scarcest resource.
In the process we call “accomplishment,” this is time.
Time is also a unique resource. Of the other major resources, money is actually quite plentiful. We long ago should have learned that it is the demand for capital, rather than the supply thereof, which sets the limit to economic growth and activity. People – the third limiting resource – one can hire, though one can rarely hire enough good people. But one cannot rent, hire, buy or otherwise obtain more time.
The supply of time is totally inelastic. No matter how high the demand, the supply will not go up. There is no price for it and no marginal utility curve for it. Moreover, time is totally perishable and cannot be stored. Yesterday’s time is gone forever and will never come back. Time is, therefore, always exceedingly in short supply.
Time is totally irreplaceable. Within limits we can substitute one resource for another, copper for aluminum for instance. We can substitute capital for human labor. We can use more knowledge or more brawn. But there is no substitute for time.
Everything requires time. It is the one truly universal condition. All work takes place in time and uses up time. Yet most people take for granted this unique, irreplaceable, and necessary resource. nothing else perhaps, distinguishes effective executives as much as their tender loving care of time.
Man is ill-equipped to manage his time.