"the person" stood for the one using an app and quietly set them apart from the one making it, as if the principles were the makers' and the use the person's. in cube design the two are often the same (selim makes mosaic, anlat and cubes and uses them), and principle 26 had just said a maker who uses the app chooses too. a design that walks the cube together (philosophy) has no "them" to serve. the line also made the principles sound like servants of someone, when the point was that they are a way of looking, not a rulebook.