Michael On Everything Else

Mental Energy

One of the things Daniel Kahneman writes about in his book Thinking, Fast and Slow is mental energy, which is good to know not only for mental health, but also physical health. I’m not sure where I read or heard it but I’m pretty sure it was David Goggins who said something like ‘your head gives up much sooner than your body.’ There’s a lot more gas in that tank than you likely think.

Back to the book. Here are a few quotes to get us started:

[A]ll variants of voluntary effort—cognitive, emotional, or physical—draw at least partly on a shared pool of mental energy.


Baumeister’s group has repeatedly found that an effort of will or self-control is tiring; if you have had to force yourself to do something, you are less willing or less able to exert self-control when the next challenge comes around. The phenomenon has been named ego depletion.


[A]ctivities that impose high demands on System 2 [conscious thinking] require self-control, and the exertion of self-control is depleting and unpleasant.

The idea of “mental energy” isn’t just a metaphor, it’s real:

The nervous system consumes more glucose than most other parts of the body, and effortful mental activity appears to be especially expensive in the currency of glucose.

(Kahneman, 2011)

This idea gives us two points:

  1. Feed your brain. Blood sugar maintenance is not just for diabetics. My wife and I have, over time, become more aware of when we need to eat in order to avoid being hangry and we’re becoming better at realizing seemingly irrational anger or frustration caused by not eating soon enough.
  2. Since there seems to be a finite amount of mental energy available, one life hack is to reduce the drain on your mental gas tank by increasing routines that reduce the need for mental effort.

We should also consider the impact of mental stress on mental energy. In a paper exploring the impact of the pandemic on mental health;

At the same time, a body of work suggests that executive functioning is impaired under conditions of fear and anxiety like those reported during the pandemic, possibly owing to the processing resources (e.g., working memory) displaced by excessive worry. For instance, anxiety is demonstrated to impair goal-directed cognitive processing thereby increasing the influence of more reflexive responses.

(Castanheira et al., 2021)

The finite amount of processing resources would include mental energy, working memory, etc. These finite resource seem to be consumed not only by mental exertion, but also through mental stress such as excessive worry and anxiety.

  1. Kahneman, D. (2011). Thinking, Fast and Slow. Farrar, Straus and Giroux.
  2. Castanheira, K. da S., Sharp, M., & Otto, A. R. (2021). The impact of pandemic-related worry on cognitive functioning and risk-taking. PLOS ONE, 16(11), 1–19.