I told my writing students about the 10,000 hours Malcolm Gladwell recommends ( Outliers), and one of them, Garland Dunlap, sent me this: 

“One becomes a beginner after one thousand days of training and an expert after ten thousand days of practice.” -- Mas Oyama, Founder of Kyokushin Karate

There is also an earlier Zen proverb which says, “Practice for a thousand days is discipline.  Practice for ten thousand days is refinement.”

Both of these ideas probably come from an ancient Kung Fu (Chinese ) proverb which says “One-hundred days of barehanded training, thousand days of spear training, and ten thousand days of sword training,” with the implication that it takes that long to master each.

All of them hold the same basic idea that it takes 10,000 days (a little more than 27 years) to truly master something.

See this.