When starting a new project, a common activity is to brainstorm & collect ideas for all the possible features and scenarios you could possibly cover. This represents the space of all the possible directions your project could go in. It is the block of marble. The true art is how you choose which features and scenarios you pursue out of this space. That is the art of sculpting the product.
All too often, this is the critical point to which all future success or failure can be traced. Along with the ability to execute on the vision, the specific vision itself is the major determinant of success. In fact, given knowledge of your team's resources and ability to execute, the vision definition is the most important determinant of success.