It is actually Anders Ericsson's[1] theory, popularized by Gladwell. Feel free to read Ericsson if you like, but he says basically the same thing, though neither he nor Gladwell ever said "put in the 10,000 hours and you will be the Tiger Woods". Ericsson has studied the realm of expert learning (for quite some time) and tries to tease apart what makes Tiger Woods, and those like him, able to attain the things they do. He has a lot of evidence that it is not some inborn talent but rather (shockingly) a shit-ton of hard work (and the quip "You'll never be Tiger Woods because your dad wasn't Earl Woods"). The book Talent is Overrated[2] is also a decent read on the topic. It also tells the somewhat humorous story of László Polgár[3], who wrote about how he was going to turn his yet to be born children into chess stars through rigorous training/practice, and then proceeded to do so.
Sure 10,000 hours isn't going to make you excellent but focused hard work can and most of the time does.
You can become good in under 10,000 hours I just used it for reference. Maybe you would have preferred this: http://norvig.com/21-days.html