"These words are no less true about indoor plumbing as they are about space travel."

“The luxury of today is the necessity of tomorrow....
    "[O]ne must first of all realise that the concept of luxury is an altogether relative one. Luxury consists in a way of living that stands in sharp contrast to that of the great mass of one’s contemporaries. The conception of luxury is, therefore, essentially historical. Many things that seem to us necessities today were once considered as luxuries. When, in the Middle Ages, an aristocratic Byzantine lady who had married a Venetian doge made use of a golden implement, which could be called the forerunner of the fork as we know it today, instead of her fingers, in eating her meals, the Venetians looked on this as a godless luxury, and they thought it only just when the lady was stricken with a dreadful disease; this must be, they supposed, the well-merited punishment of God for such unnatural extravagance. Only a few generations ago ... an indoor bathroom was considered a luxury; today the better homes of every Auckland worker contains an en-suite. A century ago there were no automobiles; then after short while, the possession of such a vehicle was the sign of a particularly luxurious mode of living; today in New Zealand even the poorest working home has his Ford or Toyota. This is the course of economic history....
    "Every advance first comes into being as the luxury of a few rich people, only to become, after a time, the indispensable necessity taken for granted by everyone. Luxury consumption provides industry with the stimulus to discover and introduce new things. It is one of the dynamic factors in our economy. To it we owe the progressive innovations by which the standard of living of all strata of the population has been gradually raised.

~ Ludwig von Mises, from the chapter “The Inequality of Wealth and Income” in his book Liberalism. Quoted by Brittany Hunter, whose words appear as this post's title, in her article 'Thank Billionaires for All Your Favourite Innovations' [edited to localise the time and place]