in the same way that when we spend our…
Keyword time in the same way that when we spend our money on one thing we can't spend it on another that also applies to time period when we spend our time on one thing we can't spend it on another. How do you value your time? You can value for the time by what you could have been doing and the money that you could have made or lost but it's also how we spend our limited time on earth. This relates to opportunity cost because when you are working on one thing you cannot focus on something else and by not taking advantage of that opportunity you have a hidden cost.
— from Time
In the book
Once you believe that in your stomach and not just your head, a second truth follows, and it is the engine of every real decision you will ever make: because the tank is fixed, every hour you pour into one thing is an hour you can never pour into another. It is exactly like money in this one respect — spend it here and you cannot spend it there. Every yes you give is a silent no to something else; you simply never see the thing you declined, because it never happened. — Time
And spend your focus where it can actually do something: the proactive put their energy into their circle of influence — the things they can affect — while the reactive pour theirs into the circle of concern, the vast territory they cannot touch, and end up only anxious and blaming. Guard it the way you guard money, because time spends the same way: an hour poured into the trivial is an hour stolen from something that mattered. And keep one old frame over all of it: everything has its purpose and its proper time and place — lakol zman — a season for working and a season for resting, each in its turn. — Decisions & Choices (Decision/Choice/Focus/Forethought/Consequences)