We cannot re-play history, but we can learn from it. If every Jewish and anti-Nazi family in Germany had owned a Mauser rifle, twenty rounds of ammunition and the will to use it. Adolf Hitler would be a little-known footnote to the history of the Weimar Republic.
Zombie Apocalypse. Chances are, you're already surrounded by mindless, bloodthirsty, half-alive, subhuman wretches. An actual zombie outbreak would just give you and excuse to do something constructive.