Sword masters regarded their weapons as extensions of their body. Because they relied on them to stay alive and earn their keep, it behooved them to be perfectly attuned to the object's shape, weight, balance and idiosyncrasies.

Presumably, this attunement between user and tool lead to the physiological boundary between the two to drop off.

Good user interfaces should produce the same result. Every interaction should be perfectly predictable, reliably consistent, and intuitively understable.