Why should you avoid using the trailer hand brake to correct a jackknifing trailer?

Using the trailer hand brake to correct a jackknifing trailer is not advisable because it may cause the trailer to skid more. When a trailer begins to jackknife, it indicates that the trailer is moving sideways relative to the towing vehicle, which can lead to a loss of control. If the trailer hand brake is applied, it can create additional friction on the wheels of the trailer, which may exacerbate the sideways motion and increase the likelihood of an even more pronounced skid. This reaction can destabilize the vehicle further and potentially cause a more severe loss of control.

The other choices highlight aspects that could be relevant in different scenarios, such as the effectiveness of the brake or potential damage to the braking system, but the immediate concern during a jackknife situation is maintaining control. Applying the hand brake could prevent the driver from correcting the trailer's path and lead to unsafe outcomes.