The "max efficiency" only does not work when you are forgetting about externalities (those are defined as "a side effect or consequence [...] that affects other

The "max efficiency" only does not work when you are forgetting about externalities (those are defined as "a side effect or consequence [...] that affects other parties without this being reflected in the cost of the goods or services involved") In your restaurant example, using "$/calorie" metric will minimize money spend, but will have a negative externality of reducing your happiness. Once you realize this, you'll want to update your cost function to something like "max(satisfaction) limit to total(calories)>needed_nutrition and total($)<budget" etc... and you can use your efficiency search again. (and then you get to third-order effects and start to think about time spent planning... Python's sort() switches to simpler algorithm for small arrays because overhead of starting up a complex algorithm is too high. The same way, you probably don't want to formulate and solve an efficiency optimization problem for the task of choosing your lunch because this is actually not that efficient :) )