Old habits die hard and being in the motor trade for over 50 years I was amazed to find out why I had so much trouble driving the new-model small cars smoothly. Driving an auto in traffic I often used my left foot on the brake pedal and right foot on the accelerator for a smooth stop/go/start operation. I have now been told by a car dealer that, in the new models, engines will not accelerate if the brake is applied.
It's not all cars, but quite common in the Volkswagen Group, because there are US regulations about stopping a runaway car in a potential emergency. Some brands use a system that cuts the engine if the accelerator and brake are hit together, interpreting it as a major drama.