How much is enough on a portrait sketch?

One of the issues that I think face most artists including myself is to know when you are finished. I think that this is a great burden for better artists more so than it is for beginners or even people that have peaked but have been doing it a long time like me.

At what point do you wrap it up and call it a day? At what point is the work finished?

Let's take this portrait for example: I had said that I was done with this a while ago. Normally the stamp that indicates that I am done with it is when I sign my name to it, which I had already done in this one. Then, a few days later, I don't know if it was from boredom or a feeling that more could be done, I went back and made some adjustments. I don't know if they are better or not but now all of a sudden this "finished" work has been put back into the work in progress stack.

I don't know if it is better with the redo, but it certainly is different. I don't think there is such a thing as doing something "wrong" in art, but in many ways I consider the original to be better, probably because it was fresh in my mind, and in many ways I consider the altered work to be better because I was able to stand back and notice things that I hadn't seen on my first go through. One thing that I had paid better attention to on the redo is that I focused more on getting the hair more realistic with the lighting. This sketch was drawn by looking at a photo so I was not drawing from memory to do this. That is a skill that I do not possess and admire the hell out of whenever I see it.

There is no lesson here, I just think that no matter what your ability level is that most artists or aspiring artists always will face this problem of knowing when they are done. I never do, and I have been doing this for a long time!