Since you are talking about this in regard to history, I would say that it means that there is no way that historians can know the "truth" about the past -- they can only tell stories that make sense to them. I tell my students this at the beginning of every new term.
Of course, this does not apply to things like "what date did the Japanese bomb Pearl Harbor." For that, there is truth. But that is not what is of real interest to historians. To historians, the real question is "why did the Japanese attack Pearl Harbor." Once you start asking this kind of question, you cannot know truth.
If I ask you why you did something that you did, you may not even know for sure. And if you tell me why, I might not believe that that was the real reason -- I might think you are tricking yourself. So how much harder is it to find the reason for a decision made by many people in a foreign culture, almost 70 years ago.
That is why history is a set of stories -- we take the story that seems most plausible, but we do not know that it is the truth.