 Why is negligence so important? Because it's a legal theory that applies in most cases to answer the question, when are you or when is a business firm legally responsible for someone else's injury? And what common law has developed over the years, over the centuries, is sort of a general rule, general standard, saying that everyone, generally speaking, has a legal duty. I'll put this in plain English, a legal duty to take reasonable precautions to avoid foreseeable harms.