The Limits of the Un-present Witness

While reading Lifton's work, I came back to a thought I've had in several other film and history classes: what are the limitations of bearing witness to an event you were not present for? In other words, how complete of an understanding can you ever have of an atrocity/situation that you were not there to witness yourself?

I'm thinking of this because I think Lifton does, in many ways, get us as close to a full understanding as can be had, but I think his limits as a witness (he was not at Hiroshima during the bombing, nor was he in Auschwitz or any other concentration camp) along with our limitations as an audience (unless I'm seriously misreading ages, none of us were alive when any of these main four events came to pass, and thus we can only look through someone else's lens) make for an interesting study in how we interpret and understand the past. Is this the best way we can understand and interpret the past, or are there ways to overcome these limitations to gain a greater understanding of the past?

In thinking about this problem, I've been coming back to Alain Resnais' film Hiroshima, Mon Amour. In the film, a French actress making a movie in Hiroshima has an affair with a architect native to the city. When she continually states she understands what the city has gone through and how destructive the bomb was, he only replies that she "has not seen Hiroshima" and "has not been to Hiroshima." The point being that talking and reading and studying can only take us so far. I guess what I'm wondering is if Lifton is taking the idea of bearing witness as far as it can go, or is there a way to take this even further to make us understand even more? How would that work? And do we think that the limitations of bearing witness as they currently stand contribute to the fact that many of these topics (genocide, American involvement in questionable wars) continue to happen over and over again?