The 10,000 hour rule was popularized by Malcolm Gladwell and substantiated by research done by Anders Ericsson. You must practice for 10,000 hours to become world class at something. There is an important caveat that you must perform deliberate practice. Spending 10 years at your desk job does not make you world class at whatever task you’re performing.
True greatness comes from deliberately working on your weaknesses and taking steps to improve. You may be a great public speaker, but your speeches lack compelling stories. Storytelling may not come easily to you so you would have to deliberately practice incorporating them into your talks. Without such deliberate practice, you may put in the hours yet still stay one-dimensional.
Deliberate practice is the part that is hardest, but also the most rewarding. It’s uncomfortable. Your mind resists you when you think about doing it, but in the end, it’s where growth comes from. Where do you need to do more deliberate practice in your life?
You will also hear that “practice makes perfect”, but I subscribe to the more definitive “perfect practice makes perfect.” Work on the right things, the right way in order to get better. This ties into finding the right mentor, teacher or coach in order to guide you in the right direction.