The first thing you should say about a thing is that it is always ‘this one there.’ It is very obvious, and so hard to notice, but the main way that things are in the world is by being distinct, by being self-contained and independent. The thing we call a ball for example is separate from the grass on which it lies and the air around it. If the ball was covered in turf, you would still recognize it as a ball, even though it could be mistaken as a spherical rising up of the lawn. This is because a ball is thingly by being distinct, by being it’s own thing, one amongst many things in the world. Things that are less easy to separate from the world around them we don’t tend to call things: trees, houses, smoke, etc.
This self-contained quality is what Heidegger calls ‘self-subsistence.’ The ‘sist’ in subsistence is again one of those ‘standing’ stems that Heidegger is fond of. So self-subsistence means that the way a thing stands forth in the world is as a standing-together, self-sufficiently, unto itself. Subsistence captures both the semi-permanence of things and the consistency of their form-content. The word relates to a strange Greek word that Heidegger mentions often ‘hypokeimenon,’ which means something like ‘that which lies under (‘sub’ in Latin means under), and so gives coherence to, what it supports.’
Again, the designer should be familiar with self-subsistence, in that the design for a thing, whether its blueprint or mold, is what lies before or under the thing, supporting its consistent manifestation in the world, all the many instances (reproductions) of that unity.