The most important thing I've ever done had nothing to do with me, and honestly and humbly, I have done my share of important things.
That's the way it goes though doesn't it? Grow up, choose something to do, and do it so well that people will see it as important. Especially you, yourself -- you definitely better see yourself as important. Lucky for you, if you don't see yourself as important our society has been inventive and has (d)evolved with new ways and tools to be important or at least feel important. There was the Stone Ages, Dark Ages, Golden Ages, and now the epic Self-Important Ages!