Spencer W. Kimball 

"We learn to do by doing." This quote is important because it's the key to all greatness. It tells us that you need to practice in order to be great at something. There isn't a secret way of doing things in order to get good at something. You need to be willing to spend lots of time in order to achieve the goals you set for yourself. An example is skateboarding. It is a very difficult and painful sport. But if you put if the years required, you can become an amazing skateboarder and even get clothing sponsors. If you get good enough, companies can pay you to skate/represent them. You can achieve this by doing what the quote implies and practice in order to achieve greatness.