What does the word "negligence" mean in a Virginia brain injury or other serious injury case?

The word "negligence" is very important in any personal injury case.  That is because, for the plaintiff to win a personal injury case, it is usually necessary for the plaintiff to prove that the defendant was negligent and that the defendant's negligence caused the plaintiff's injury.  In Virginia, as elsewhere, "negligence" means a failure to exercise what is called "ordinary care."  Ordinary care is that degree of care that a "reasonable person" would exercise under the same conditions and circumstances existing at the time and place of the incident in question.  I know this sounds like a lot of legal gibberish.  But what I've just written is pretty much what a jury is told about the law before the jury is sent back to the jury room to decide the case.  In fact, the actual jury instruction read to juries every day in Virginia is as follows: "Negligence is the failure to use ordinary care.  Ordinary care is the care a reasonable person would have used under the circumstances of this case."  So there you have it.  What does it mean, exactly?  When thinking about the "reasonable person" in layman's terms, I tell people to imagine a slightly nerdy fellow with a pocket protector who is very careful about things as he goes about his daily activities.  Is the speed limit 55 miles per hour?  The so-called "reasonable person" goes 55 mph or below, but not so far below to be "unreasonable."  (We've all seen people driving 35 in a 55 zone, which I would submit is unreasonable and negligent.)  Is there something slippery on a floor in a grocery store?  The reasonable person who works at the store looks for that sort of condition and, when he finds it, he cleans it up or puts down an effective warning sign.  You get the picture.