Science is to say. Orbits can be calculated very precisely, and there's only one chance in 4.7 million that 2012 DA14 will hit the Earth within the next century.
A friend of mine whose husband is an asteroid expert pointed out on Facebook that close flybys and atmospheric explosions like this happen every single day -- it's just that most of the explosions are smaller or happen over unpopulated areas, and most of the flybys are by smaller objects that don't get as much advance notice. The coincidence is not that these things happened within a day of each other, since that's actually pretty commonplace; the coincidence is that they both got so much notice.
Oh yes, I am aware of that... we have all kinds of debris entering the atmosphere every day. It's a wonder that our satellites and international space station haven't suffered more damage than they have at this point. Even a pea sized piece of rock flying at 50k mph can easily rip a hole right through the metal walls of our crafts, and there's nothing you can do about it (no laser tracking computer that can pulverize the debris before it hits).
I also understand that orbits
can be calculated precisely, however there is always a margin for error when it comes to passing objects. We can't accurately predict how other gravitational forces will affect the object, including this present passing. As Sojourner pointed out, the asteroid will experience a change to its path due to the gravitation forces from Earth on this fly-by. They may be able to predict if it will bend it in such a way as to bring it closer or further away on the next pass, but I don't believe they can make an accurate estimate on the exact distance it will pass next time. Even this time, there was open speculation on whether or not a satellite might be damaged since it passed inside the ring of geosynchronous weather and communications satellites. If measurements were truly precise, they would have been confident to say there was no possibility of a satellite being damaged.
Relatively speaking, for a passing object to fly within the ring of geosynchronous satellites is EXTREMELY CLOSE compared to the orbit of the moon. I wonder how much advance warning we'll have with a larger object, say of 3x the size. Something like that could cause a massive disruption to our environment and extensive damage to life and property if it landed in a densely populated area.