I don't know if you're young, obviously, but this is a young, or at least unattached, person's point of view. I taught myself to program in the 80's when I was in my early 20's. In my later 20's and through my early 30's I did it for fun and profit, often working on a project 14 or more hours a day. By the time I got into my early 40's I had a wife, three young children, a house, a couple of pets, etc. to go along with the job. Suddenly, or perhaps not so suddenly, there were a great many demands on my 18 hours per day of waking time. Unless you're different from most people this is how it will likely proceed with you as well. So one way of looking at this mantra is "we want young, unattached people who will throw themselves into their work and not coincidentally do it for less money than a middle-aged person with a family."