That's the magic number, as far as brains are concerned.
Even before diving in to Outliers, I'd heard the number before. It goes something like this: in order to master something (and I mean You are the Shit, the Bee's Knees, recognized for what you can do) you need to practice it for ten thousand hours. That's when the brain flips a switch and says "Ok, this? We've got it." The difference between good and great isn't just practice. It's many, many hours of practice.
Ten thousand hours works out to be about eight hours a day, seven days a week for four and a half years. Without a vacation. For most people, though, it works out to doing something for about ten years. Nine, if it's chess and you're Bobby Fisher. I wonder how it falls out with chefs, though. And I do mean Chefs - the real thing. Because yes, I imagine that if I am still at this job after four more years, I will be pretty well set in my laminated dough skill set. Less that that, even, because well, the crazy hours cooks can keep. But what about the rest of the products? Menu creation? How does 10000 hours translate into the development of one's palate? Do you need to taste things for ten thousand hours before you can really tell what is sublime? And then do you need ten thousand hours of plating techniques?
All I know for sure is I've been cooking professionally for five years now. I still have a lot to learn. But I think I've got scooping cookies down.