The Nurse Log Principle
Sustainable systems design death into life, transforming waste into wealth, and closing loops so outputs become inputs.
Sustainable systems design death into life, transforming waste into wealth, and closing loops so outputs become inputs. When nutrients or resources flow in one direction - from environment to organism and then lost from the system - the system depletes its resource base and collapses. When nutrients cycle - with outputs from one process becoming inputs for another - systems achieve sustainability, persisting without external subsidy.
When to Use The Nurse Log Principle
Apply when designing systems for long-term sustainability, transitioning from linear to circular resource flows, reducing waste, or creating regenerative business models. Especially relevant when resources are scarce or when waste disposal creates costs or environmental harm.
How to Apply
Map Current Resource Flows
Identify all inputs, transformations, outputs, existing loops, and leakage points in your system. Create material flow diagrams (Sankey diagrams) to visualize where resources enter, transform, and exit.
Questions to Ask
- What materials, energy, and resources enter your organization?
- How are inputs transformed into products or services?
- What outputs leave the organization and where do they go?
- Where do outputs cycle back as inputs?
- Where do materials leave the system without recovery?
Outputs
- Resource flow map
- Leakage point inventory
Design Circular Loops
For each leakage point, design interventions to recover and reuse resources. Distinguish between technical cycles (durable materials) and biological cycles (biodegradable materials).
Questions to Ask
- Can this material be recovered and reprocessed to near-original quality?
- Should this material return to biological cycles through composting or digestion?
- What take-back, sorting, or reprocessing infrastructure is needed?
Outputs
- Loop design specifications
- Infrastructure requirements
Innovate Business Models
Shift from selling products to selling services, retaining ownership and creating incentives for durability, repair, and recovery.
Questions to Ask
- Can we offer product-as-a-service instead of ownership transfer?
- How can we capture products at end-of-life?
- What leasing, subscription, or take-back models apply?
Outputs
- Business model options
- Revenue model redesign
Overcome Barriers
Address economic, technical, behavioral, and systemic barriers to circularity through value capture, technology investment, education, and coordination.
Questions to Ask
- What cost premiums exist and how can we capture value to offset them?
- What technical constraints limit recyclability and how can design address them?
- How can we shift customer behavior toward circular options?
- What value chain coordination is needed?
Outputs
- Barrier mitigation plan
- Partnership requirements
Measure Progress
Track material circularity indicators, product circularity metrics, business model circularity, and absolute system-level impact.
Questions to Ask
- What percentage of inputs come from recycled/renewable sources?
- What percentage of outputs are recovered/recycled?
- What is our hemorrhaging rate vs. single digits?
Outputs
- Circularity metrics dashboard
- Progress reports