When to stop?

The struggle over how much to say, the memory, in my ear, of Dorothy Eisner telling me not to model.  The way people like a particular painting that painted itself ... I took my pastels into the room with the loved painting and drew on top of a scan of where I'd got to on this painting in the hope of finding what should happen next, wondering if the loved painting would offer answers. Back in the studio I didn't look at the pastel result as I worked, but it had warmed me up, probably. Later I compared and took from the pastel what seemed to be missing. Still not sure if it's finished.