This is what can cause forgetting the handbrake when parking your car.
There is obviously a good reason why cars have a handbrake. Once left stationary, a car can move on its own if its wheels are not properly locked. When going downhill, forgetting the handbrake is instantly noticeable. But when the ground is almost flat, the danger represented by this oversight is only noticeable after a few seconds or minutes.
This video illustrates the problem perfectly. Filmed by a CCTV camera at a gas station in Thailand, it shows a white Mitsubishi pickup parked near the pumps. But over the minutes, it moves slowly until it hits the black pickup that was trying to fit into the traffic.
The driver of the black pick-up then gets out of his vehicle and finds that the other vehicle does not have a driver. This is a funny situation to say the least …