A plaintiff can usually sue a defendant only if that defendant was the one who hurt the plaintiff. In many cases, it is easy to figure out who hurt someone. But sometimes people get hurt in ways that nobody expects. For example, a defendant might be driving while drunk, and he might hit an electric pole. The electric pole could fall down and cause a neighborhood to lose electric power. As a result, a person two miles away might trip and fall in the dark. The law will decide whether the drunk driver "caused" the person to trip and fall.