It is related to torque. If the power block is as big as the force block, you will step on it quickly and the car will move slowly.

Let's put it in plain English.

Let's assume that the gear position at the pedal is A and the gear position at the rear wheel is B.

therefore

Big A+ small B is laborious, but fast.

Small A+ big B saves effort, but it is slow.

Just like the transmission of a car:

The starting gear is equivalent to A+ big B.

In high gear, it is equivalent to A+ small B.