That&#x27;s simple.  You tax sitting on money not earmarked for a recognized task (EG: Saving up for big investment X (named) such as college, a new home&#x2F;building, etc.) or for rainy day funds; but you also limit the maximum that can be stashed for such tasks.<p>Then with that tax you re-invest in infrastructure, exploration of new resources, and even missions to space.  (I&#x27;d rather we have a (robotic) mission to the asteroid belt than mars...).