An accident is an event. Negligence is a legal basis for holding someone responsible for an event.
Some injuries occur even when everyone used reasonable care. Other incidents happen because a person or business failed to take precautions that a reasonably careful party would have taken under similar circumstances.
The question is not simply whether the defendant intended to hurt someone. Most negligence cases involve unintentional harm. The central issue is whether the conduct fell below the level of reasonable care and caused the injury.
