What might happen if the brake were applied strongly going downhill?

If the brake is applied strongly while going downhill, it can lead to a loss of traction, causing the wheels to lock up. This can result in skidding, making it difficult for the driver to maintain control of the vehicle. Additionally, excessive braking can cause brake overheating, leading to brake fade, where the braking efficiency decreases. Ultimately, this could increase the risk of an accident.