A new way of thinking about effort is in terms of opportunity cost. In the paper "An Opportunity Cost Model of Subjective Effort and Task Performance", Robert Kurzban and co-authors argue that certain parts of your brain can deploy many possible functions.

However, the executive will limit the number of simultaneous tasks and apply it only to the most valuable activities. This experience of the cost-benefits will feel like effort. When your current activity doesn't feel like a good use of your limited mental bandwidth, you feel like doing something else.

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.

How effortful something feels will depend on what else is available. It is more effortful to work with an alternative nearby, such as your smartphone to browse Instagram instead.

If we see effort as a comparison of alternatives, then habits - automated behaviour - can reduce the desire to reach for a substitute.

In the opportunity-cost framework of effort, when you get rewarded for an effortful activity, the experience of effort becomes less unpleasant, meaning we can increase our self-control by remembering that certain actions yield positive results.

If persistence in doing a difficult task pays off, you'll find it easier to endure in the future.

The willpower to do a specific activity depends on learning the value of the activity itself.

The opportunity-cost theory suggests that if you can establish that a particular activity is rewarding compared to alternatives, it will become less effortful.