I'm currently reading The Black Swan, by Nicholas Taleb (which I highly recommend simply for its thought-provoking ideas). In the book, Taleb makes the argument that what we don't know is far more important than what we do know (a little over-simplified, read the book to get the full concept), which leads to an interesting idea which can be of comfort to some and disheartening to others. The men and women studied in history are people who did great things, but what of the people whose little actions have a huge, yet indiscernible, impact? If a Boeing employee proposed higher safety and hijack-prevention standards for their planes in early 2001, 9/11 may have been avoided. Yet no one would ever thank this man, nor call him a "hero" for preventing a terrible attack, because no one would ever be able to comprehend the impact of his actions. 9/11 is referred to by Taleb as a Black Swan; it was something that could not be expected, had a large impact, and forced people to look at and analyze the "what ifs."

You may never be remembered for great things, but a small action of your own doing could have a great impact. You could be an "unsung hero."