[Okayyou]

The quote is from Henri Cartier-Bresson but is pretty well repeated on the internet today. Generally I think it is more applicable to pro photographers that shoot every day. It also depends on how general you are with your subject matter. If you only shoot architecture you probably don't need 10,000 shots to figure out how to make a good image. And if you've shot 20,000 buildings it doesn't mean you can jump into sports photography like a pro. However there is probably some number of shots it takes to really understand a camera, I'd guess a couple thousand.