Levels
- Men
- Horses
- Saddles
> The more important [invention] was the saddle, which arrived in the West as a barbarian innovation in the first century after Christ, and which gradually replaced the older horse-blanket and riding cushions. The saddle, with its rigid frame, although it did not add to a rider's lateral stability (a presupposition of mounted shock combat), nevertheless helped to prevent him from falling over his horse's tail.
> Medieval Technology and Social Change by Lynn Townsend White
- External Combustion
- Internal Combustion
- Automatic Transmissions
- Electric Vehicles`
- Self-driving vehicles

The trend is away from 'relational' and towards 'transactional'.
If you reject the good you were given, a void is created and you seek to fill the void