What, you think it's going to sneak up on us from behind the sun?
They're space objects.
They're not that smart.
Actually, that is what they think can happen. It isn't that they (stuff in space) aren't that smart, it is that we can't see. We can only track something like .3% of all NEOs, and that is not counting somethign that gets knocked our way either out of the Asteroid belt, or even further in the Oort Cloud. So, yes, we have more of a chance to be whacked by something we didn't see than by something we do, even if it is large.
I think that we should worry more about the fact that a giant asteroid is going to hit sometime soon...or a massive volcano explode soon.
I have odds on the yellowstone Super Volcano going up, completely destroying North America out-right and destorying the ecosystem killing the rest of us within 100 years (It is actually already past its figured eruption date).
Second on nuclear holocaust, after all humans are idiots.
Third on the sun, be it solar flair, radiation or whatever.