Originally Posted by Frank Reiner

The appropriate division of any gear ratio spread is a function - in its simplest form - of vehicle weight, available power, and required operating speed range of the vehicle.

A light vehicle with relatively high power may operate satisfactorily with 2 speeds.
A highway tractor pulling doubles @ 60,000lbs will often have 16 speeds.

As Lloyd Price put it in "Stagger Lee" - "poor man, he threw eight!"
If Billy had thrown seven he might have lived.