The following must have happened to everyone: You are expected to finish something by a certain date & time, and you fail to do so. When someone asks you why, you say "Sorry, I was too busy, I didn't have time for that"

But in many - if not most - cases, that's an inaccurate statement. You had plenty of time (in terms of actual available hours or days). You had time to come home and sit on the couch, read a book, watch TV, play a game, talk to some friends, etc. What you didn't have was the energy to work on that task.

In order to complete a task, we need two things: time to work on it, and the energy to work on it. ('Having energy to complete a task' can refer either to a general level of readiness/vigor to do work or complete tasks, or to a specific level of willingness/desire to complete a specific task). If you have all the time in the world, but no energy, you can't finish the task. If you have all the energy in the world, but no time, you again can't finish the task. What you need is both.

So, I propose a new term to capture this fact: etime.

In some sense, etime is like the product of your available time and energy. If you have no etime (either no energy or no time), then you can't accomplish anything. You can accomplish a decent amount of work if you have an adequate amount of etime (a lot of energy and little time, or a lot of time and little energy, or medium amounts of both) and you can accomplish a ton if you have a lot of etime (a lot of energy and a lot of time).

People today use the amount of time they have when explaining whether they can finish a task or why they weren't able to finish a task, but that is inaccurate. Etime captures the situation much more accurately.

Now when someone asks you why a task was not finished, you can accurately say "Sorry, I didn't have etime for that". Or, you can ask someone "Do you think you'll have the etime to finish this project by the 15th?". Or, in response to some requests, you can say "I don't have etime for that".