I see it in my mind.

That's a familiar lament. One thing I figured out is that I can almost never get what is in my mind exactly on paper -- but if I try hard enough, later when I get some distance what IS there is pretty cool. This is why I often can't stand something I'm working on when I'm working on it, and then come back to it later, after the initial mind-image has been erased, and really like it on its own terms.

Anyway, I think its a universal artist's lament.

Yeah... it drives me crazy. I know I should stop but I just can't help myself.

I think that's maybe a graphics/illustration/design problem? where you have a much clearer picture in your mind of the finished piece.

I have certain ideas of what I want the painting to be like but it often takes on a life of its own and evolves very differently in response to colours and marks and accidental stuff. (talking more studio large paintings here than plein air work).

I'm working on a series of landscapes now, where I wanted the colours to be primarily reds and the image semi abstract. The paintings are about making it work and I had no clear cut idea of the finished pieces when I started - one of them keeps changing dramatically in response to its needs (if I put a flash of cadmium here then it needs a touch of dark there to balance it etc etc etc)