Computer Time Sharing Metaphor

Effort is the experience that what you're currently doing is not worth it.

It's like computer time-sharing. The computer resources don't get used up, but they are limited. If you want to do something like running a major background process, like a backup or rendering operation, and want to play a game, you have to decide to shut it off or wait until it is finished.

The opportunity cost model is similar, except that opportunity costs are experienced as effort.