An artist is... An artist does...

Fulfilling.  Inspiring. With vision. Motivated. Driven. Ambitious. Aspirations.

 This hand painted "birdhouse" took a few treatments of color, distressing and attention to detail before it was ready to sit outside in the elements. When is an item actually completed?

How does one know it is ready?

These terms all seem to describe or identify characteristics of an artist.  The desires of one that knows what they are looking for in the finished product.  When is a project done, completed or finally meeting the standard?  In many situations, there is a definition for perfection.  Rules apply. Laws govern. Manners dictate.
On the other hand, an artist is often times ahead of the curve.  Separate from the pack.  Different from the crowd.  Unique.  For instance, consider Michelangelo up painting The Chapel ceiling.  Maybe laying there on  a scaffold system, bringing all his supplies up and working from 8-5, coming down and washing up for dinner.  It might not have happened like that.  Consider this as a possibility:  He heads up the ladders and paints till he his exhausted.  Takes few breaks.  Reduces his food and water intake to minimize bodily interruptions.  His co-workers probably couldn't get his attention by any means, even promising a good meal.  He was driven to complete the task till it matched the vision in his head.  He was an artist!
What drives you?