@MutoShack@functional.cafe Trains don't need tires. A 4 wheeler is more robust, but some applications might call for 3, 2 or 1. The quickest decision is a leap of faith and the safest is being idle. There are always trade-offs and people don't like when you make decisions for them. The key is to find and expose the lowest common denominator abstraction, the wheel. Imagine a concept of a car without a concept of a wheel. How bizarre would that be. Many such things in our industry.