Everybody needs to experience riding one of these 18 or 20-speed bicycles up a long, steady up-hill grade. (Like running against the wind at Bonneville)
Just keep going up (lower numerical, faster speed ratio) in gears, and real quickly you get the idea of "running out of horsepower and / or torque.
Put it into the 'tallest' gear you've got, and you will probably come to a complete stop!