a) In walking, the energy and movement generated stem from the person. When running, simply more internal energy is generated.
b) In driving a car, the main resource is external, the car itself, while the driver expends minimal internal energy;
c) Skateboarding rests between these extremes. On the one hand, a skater must keep himself in motion by pushing with his foot, yet, motion is made much more efficient owing the lower friction levels in the mode of travel.
A similar pattern exists in the mental sphere:
a) An individual can make calculations solely using his own intelligence and brain energy to propel the process;
b) he can use a computer to do all the calculating;
c) he can learn and apply mathematical principles to make the thinking process more efficient. The product joins internal and external resources.
Each mode has its pros and cons:
Efficiency: b) is more efficient than c), and c), more than a). To use b) is to have minimal personal input and maximum output. But excessive reliance on external resources can result in the atrophy of mind and body.
Exercise: a) exercises one's mind and body the most; c), less so; and b), the least. However, to use a) as a main form of productivity is to have enormous personal input with relatively little output.
Harmony: b) offers the most sustainable form of functioning being relatively efficient while providing exercise. It offers the greatest balance between external and internal resources. To use b) is to have balanced input and output.
All three modes of operation are important and have their place in human endeavour. However, when faced with relatively straightforward calculations, why use a calculator? Use your brain. When travelling short distances, why use a car? Skateboard instead...