Why should the trailer hand brake not be used while driving?

Using the trailer hand brake while driving can indeed lead to skidding, which is a result of sudden engagement of the brake system. The hand brake is designed primarily for securing the trailer when it is stationary, and it applies pressure to the trailer wheels independently of the towing vehicle's brakes. When engaged while the vehicle is in motion, particularly in emergency situations or during tight maneuvers, it can cause one set of wheels to stop suddenly while the others are still moving. This discrepancy in wheel speed can lead to loss of traction, making it much more difficult to control the vehicle and increasing the risk of skidding. Maintaining control is crucial for safe driving, especially with larger vehicles that can have significant stopping distances and stability issues.