A clear 5mm boundary.
Inside the glass is my son, fleeing into a pixel universe away from the rain. Outside is my daughter, embracing the damp world, running free.
Yet, the boundary shifted. My son broke out to join the falling petals, while my daughter, tired, retreated into the dark cocoon of the car. A perfect reversal. Their universes crossed but never merged; the 5mm remained intact.
Yet, it is only because of their profound family bond that they can immerse so deeply in their own worlds. It is a beautiful, affectionate distance.