How about an arrow attack? An arrow hits the Fighter for 3 damage. Realistically, you get hit with an arrow, you're as good as dead. But this is D&D, and not all is as it seems when hit points come into play. According to how D&D views hit points, this might not be a hit at all. Maybe you dodge out of the way, or luck came into play. You exert some stamina for getting out of the way in time, and this is represented by taking off 3 hit points from your total. But what if the arrow is poisoned? Now you have to make a save. So if the arrow missed you, it didn't really miss you.