I always thought of the left pedal as the GO-Pedal, the right pedal as the Slow down Pedal, and the middle pedal as the Go Back-pedal. The lever on the left is the hold & release lever with emergency stop when all else isn't cutting it.
Folks that drove model T cars hard and fast, got used to stomping the right pedal and grabbing for the E-brake lever when they needed to slow down in a hurry. Folks that drove them with safety in mind tended to be more mindful of anticipating their slow down actions early and were more apt to adjust the throttle more carefully then ease into braking for stops. If a person has ever driven a horse and buggy, they tend to anticipate things better but they also don't expect to get there in a hurry.
When the left pedal became the clutch release pedal in later model cars like the model A, I wonder how long it took folks to get used to the change over. In the model A cars, the Go-Pedal changed all the way over to the right side so it was sort of a big switcheroo on new owners of model As. At least a person no longer needed three arms to drive the car.