Opportunity Cost: Time
Fragments from imaginary dialogues
“Opportunity Cost is a very useful model from Economics. There’s a hidden cost to everything we do. The cost can be monetary (money spent on one thing is no longer available for something else), but it equally applies to any other resource, most notably, time.
Time is the most valuable resource because it is nonrenewable.
Time wasted is time no longer available for doing the things that are truly meaningful, that make you feel vibrantly alive. Opportunity Cost.”
“Makes me think of a quote by Robert Greene:
There’s only two types of time: dead time and alive time.
“
“I love Robert Greene’s vivid distinction.
The expression ‘killing time’ is so accurate.
Dead time never returns.”
“But neither does alive time.”
“The difference is, alive time enriches you.
Both dead and alive time compound.
Little by little by little they add up. The effect is invisible at a smaller time frame, in the same way a tiny little drop of water feels insignificant. But at a larger time frame, those tiny little drops can carve mountains.
The difference is, one adds to your life, the other takes away.”
Dani Trusca 
This is a very important concept that I wish more people could truly internalize. Understanding this helps us to prioritize positive actions, keep neutral actions (or inaction) to a minimum and avoid self-destructive actions like the plague.