Become An Expert

I've been reading This Is Your Brain On Music.

The author notes that many people have found that you can become an expert in anything if you devote a minimum of 10,000 hours to it. That includes music, sports, chess, and so on.

Assuming a 40-hour week, you can become an expert at something in about five years. If you're not working at it full time, figure three hours per day for ten years.

I've probably spent more than 10,000 hours with Excel, so that explains why I'm an expert. If I continue my current pace, I will be an expert banjo player when I'm 64.

What have you spent 10,000 hours doing? Did it make you an expert?