A big space rock colliding with Earth, what are the odds?

I don't know about you, but I've certainly seen enough disaster movies about this scenario. A great big rock is flying through space and its target is planet earth. We've seen variations of it on screen. I've certainly read variations of it in books and it's an issue that you actually have to seriously consider. 

Admittedly space is huge so what are the odds of a large asteroid striking the Earth? Believe it or not, NASA actually games this out with their fifth biennial Planetary Defense Interagency Tabletop Exercise in April. Then on June 20, NASA unveiled the results. 

according to ndtv.com,
“The Tabletop exercise summary noted, “During the exercise, participants considered potential national and global responses to a hypothetical scenario in which a never-before-detected asteroid was identified that had, according to initial calculations, a 72% chance of hitting Earth in approximately 14 years.”
To be precise, “72% chance of Earth impact on 12 July 2038 (14.25 years warning time).” 

The basic summary states that we are just not prepared. We're not prepared to make the necessary decisions. We're not prepared with any kind of technology to deflect these, Rocks. (Although we're starting to do research.) 

The main thing to keep in mind at this point is that there are no known asteroids of significant size heading anywhere near Earth. And keep in mind that this is just a theoretical exercise designed to help us learn what we don't know about and how to deal with this situation, if it ever occurs. 

Basically, chill out. We're not talking about the movie Armageddon turning into a history lesson.