It&#x27;s a bit of cognitive load. It&#x27;s not clear whether or not [1,2] + [3,4] should equal [1,2,3,4] or [4,6].<p>Keeping track of that, (oh wait, this is a numpy array, not a python list...) and things like that expand the amount of the language that a programmer must keep in her head at any one time, and are the definition of complexity.<p>There&#x27;s no known silver bullet for the complexity &#x2F; power tradeoff, which is why we get so many cool languages!