Design as a discipline gets so bound up with particular domains (architecture, software design, product design, industrial design, urban planning, ergonomics, quality management, etc) that fundamental concepts of design can sometimes get obscured. One of the most fundamental design concepts is ergon, which is a Greek term meaning work or activity. You probably guessed that the word ergonomics is rooted in this term. But ergon is not limited to workplaces, as is ergonomics.
An ergon is an activity or function essential to any person or thing. It is a concept as old as Aristotle, who wrote that just as a knife has an ergon of cutting, so a flute-player or sculptor each have a distinctive ergon.
Good design always requires first analyzing activities to find the essential ergon, and then designing artifacts (e.g. buildings, software, processes, etc) that don't inhibit or distract from this ergon, but that get out of the way and enable one's ergon to be done well. The key concept in ethics since Aristotle, virtue, is defined in his Ethics as "excellence in performing one's ergon". So, whereas a virtuous, quality knife is one the cuts well (it performs its ergon well), so the virtue of a flute-player or a sculptor is to perform their distinctive ergon well. The designer is thus in the business of enabling people to flourish by performing well the activities and functions essential to them, and sustainable businesses are built on products based on such designs.