It hangs in the Spurs locker room and is the motto, or creed, by which they approach their business of winning basketball games. And, more importantly, the method by which the approach the business of winning championships.
One can read this simply. If you think of the stone cutter as skill-less laborer whacking at a rock mindlessly until it breaks. You can then approach your business in the same way. Just work, work, and work some more. And eventually success will happen.
But, if you view the stone cutter as a skilled professional. One who delivers each blow with an intention. Then, the quote has a lot of depth to it. Success is the result of many decisions implemented precisely. Even though many individual decisions may not have a measurable result, it still plays an important part of the success.
Additionally, the message is that there are no shortcuts. Success is the result of working to be better everyday. One day at a time. If a day shows no success, you have to keep the goal in mind. Every day should be executed toward that goal.