The accounting boundary explains why one participant can become genuinely healthier while the field it depends on grows weaker. Every ecology counts some things as part of itself — a firm counts revenue, growth, and market share — and whatever falls outside that circle (labor displacement, systemic risk, eroded trust, drained safety margin) appears nowhere in its measure of health. So the smaller the boundary, the easier it is to look excellent while exporting the cost elsewhere; from inside the local system, everything genuinely looks fine.
It is a broader idea than the economist’s externality, because the exported cost need not be a price effect at all — it can be lost traversability, a depleted commons of field conditions, or reduced global redundancy. Its cleanest statement is the deep pattern of the whole phenomenon: local ecology becomes globally destructive when its boundary of responsibility is smaller than the boundary of its consequences. The corrective is to make the two the same size — the work of ecological subsidiarity and of ecological transfer accounting, which drags the exported cost back onto the ledger.