What Benjamin meant was that how we act in the present can change the meaning of the past. The past may not literally exist (any more than the future does), but it lives on in its consequences, which are a vital part of it… In one sense, we know more about the French Revolution or the Stalinist reign of terror than those who were involved in them, because we know what they led to. With the privilege of hindsight, we can inscribe these events in a broader narrative, making more sense of them than Robespierre or Trotsky were ever able to do. The price of this superior knowledge is impotence. There is no way we can use this knowledge to undo past catastrophes. We are like men and women frantically waving at history from a long way off, powerless to intervene in its crises and convulsions.