When is a painting complete?

This seems to have been a burning issue amongst the group lately as we heard along the grapevine that Laura didn't seem to think any of our large paintings of the still life were finished, which of course, being more experienced maybe she noticed things we didn't in our work.
I feel that this is a very SUBJECTIVE issue as the artist may intend to paint something in a specific way which may arouse the issue in its viewers, critics, that their work isn't finished.
When i think about my piece, posted below, i know i really wanted the background to be minimal and keep the focus on the 'figure' (if you will) but after hearing that it wasn't apparently finished it made me think twice to reasses the painting.
Ok so i have followed the criteria, i've filled the canvas, got the image on there and done a tonal black and white representation of the image.
The criteria, which i am reading now states 'pay special attention to the relationship between the object and the background and the definition of the edges'.
Now some may argue i have drawn the image on and used charcol to define the edges, and that they are 'no such things as outlines' but i wanted to keep quite a drawn feel to the image. In fact it was only after the application of paint did i use the charcol, i started out with a wash of oil which outlined the object.
Anyway, over Easter i am going to look at the piece again and see what else may need doing to it.....my only concern with the background is that when i've seen other members of the groups work with full background, it has distracted from the image, which i really don't want to do as i feel i have produced a strong piece.
SO when is a painting finished?
Well, from experience, it is when i feel i have come to a point where anymore work would spoil it and know i have sometimes pushed this boundary too far and ruined previous works.
I take a step back and constantly reasses my work and keep revisiting it, a few days afterwards sometimes for a fresh outlook.
Sometimes you just get a feeling about your work, like an intuition that it needs 'something' more. But i can't give a definate answer, not because i don't know; maybe i don't know how to express what i mean, but my main reason is that you have to take into account the artists's intentions, who are we to question their work? We can give a critical response and an analytical response, but we cannot account for their reasonings.
Yes, we have been given a criteria to follow, but as artists do we have to follow this inclusively? Or is there room for indiviuality and personal response?
It's all pretty confusing, as i dont believe there is a definate answer to this, i just think you know in yourself, as an artist, knowing your own intentions...
Until someone comes along and tells you otherwise............