If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled, or composted, then it should be restricted, designed or removed from production.
Common or bulk materials means lots of supply, which means low cost and high availability. Don't force builders to search out substitutes.
Parameterized designs allow to be flexible and adaptable
Modular designs are easy to repair and remix. Damaged components can be easily swapped out or repaired
So they are easy to service. Prefer low-wear and low-failure prone components, materials and designs.
The most reliable component is one that doesn't exist.
Designs should be implementable without having to remake the earth or having to learn an entire field of study. If you do ask your user or builder to learn something, make it something high-value.
A conceptual model is an explanation, usually simplified, of how something works. Completeness or accuracy is less important than usefulness.