Wears out the motor.

You don't want to do that." "I see," said Hurstwood.
He waited and waited, while the man talked on.
"Now you take it," he said, finally.
The ex-manager laid hand to the lever and pushed it gently, as he thought.

It worked much easier than he imagined, however, with the result that the car jerked quickly forward, throwing him back against the door.

He straightened up sheepishly, while the instructor stopped the car with the brake.
"You want to be careful about that," was all he said.
Hurstwood found, however, that handling a brake and regulating speed were not so instantly mastered as he had imagined.

Once or twice he would have ploughed through the rear fence if it had not been for the hand and word of his companion.