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See my previous post.

We don't often see something this big, this close. (You could just about observe this with good binoculars. It's been a few years since that happened.) The object was picked up by an essentially amateur survey in Brazil, and then we got lucky that observers who usually aren't looking for rocks noticed a fast-moving object in their images. (_And_ that they observe from two separate observatories in Texas and Hawaii. They probably do that so they can confirm variations in star brightness aren't just some local issue, but in this case, it meant we got some parallax.)

Data on incoming objects, including this one, are publicly available and discussed. We've had one hit us (2008 TC3) where we had enough data to puzzle out where it was going, and tracked it right down to where it hit in northern Sudan. (It was only a couple of meters across, so no danger... though you'd have seen one heck of a meteor if you'd been there.) Because it was so small, we had about 17 hours of warning on it. Generally speaking, you'd get more warning with bigger, brighter objects, but not always (didn't happen this time, for example; we really got somewhat lucky with TC3.)

True, we can't prevent/mitigate an object hitting the next day. Had we been able to predict Chelyabinsk, though, we could have said : "An object will hit at exactly this place at exactly this time. Leave your windows cracked open. Don't stand near things that might fall on you." For a larger object (assuming correspondingly larger lead time) : "You might want to be somewhere else that day." Or -- for the 75% case of water impacts -- "Don't go to the beach today."