It's a struggle. A balance really. Each time sacrificing something in order to achieve something else. Most often it's time, but that is only the high level obstacle. It's the foresight into how much time it would take to achieve the ideal. It's the choices taken along the path to the ideal that makes the goal more and more obtainable.
It's knowing what sacrifices are reasonable to take. The ones that allow you to push still closer to the ideal, but at the same time make the goal obtainable.
I wonder how to know when something is great. Perhaps, if your asking, you're not there. Good. Good is easy. It's that extra effort, that extra insight, that pushes something from good closer to great.
When is something great? Not when you find yourself reluctant to share it. At the same time, however, keeping something locked away from the world may keep it from judgement, but also from knowing greatness, or allowing you to discover a previously unseen path. A step, that moves you further down the continuum toward greatness.
Why, when good is good enough, should you struggle on toward greatness? I guess it all depends on the end goal you seek.