For the painter, who may take months to finish a work, it can be a difficult thing to see an audience spend only a few seconds looking at the finished piece before moving on. Blood, sweat, and tears can go into a work, and an artist will often pour their heart and soul into their creations, forgoing proper eating, relaxation, and sleep in a bid to achieve a finished piece.
Likewise for other art forms. Music, film-making, and even photography (which can sometimes have a lot of pre and post production work outside of the "click" of a shutter). Art takes time, and for the artist it can be all-absorbing. This is the process. This dedication and care is what creates the wondrous things that we see all around us, from the chair that's been designed by the chair-maker, to the building that's been crafted first on paper. Time and more time are the main ingredients to art.
So, when a piece is finished, most artists will feel an emptiness. Where once there was incredible dedicated effort, there is now a nothingness. Sometimes it can manifest itself in a type of depression or withdrawal, where an artist will seem to skulk, or become ill-tempered. It's ok. All loss is like that, and coming to the end of a journey is a process in itself, one which every artist needs to learn to deal with.
Creating an artwork is in itself an art-form, a head-space. But each piece is unique, and requires it OWN unique head-space, one which will never be lived again. One chapter, one work. We all have to deal with it, and we all have our own ways in which we discover it, live it, and let it go. It's not unlike a temporary love-affair, one which invariably comes to an end.
The upside is usually that one can share their piece with others, finally, after so much has been poured into it. We all hope that you feel something from it. I know i do...