That's actually how people with executive function disorders (like ADHD) describe it. There's a finite amount of gas/fuel/internal liquid they have in a day, which gets consumed as demands are made of them and it runs out a lot sooner for them than it does for others. Once it's gone even simple tasks can be overwhelming. Taking that one step further is the "spoon theory" (https://neurodivergentinsights.com/blog/the-neurodivergent-s...) which divides that finite resource into categories like mental, emotional, physical, social, etc.