For me, the last 10% of a painting usually takes 90% of the time spent to complete a finished piece. But it's those last few brushstrokes, subtle temperature shifts, and minor design changes that can take a painting from being good to (hopefully!) being something that really grabs the viewer and leads them in. Every plein air piece that I paint gets to about the 90% stage outside; it's back in the studio, when I'm away from the scene, that I can judge what the painting needs to be a better work of art, instead of being overwhelmed and over-influenced by the scene in front of me. Even when a painting fails outside, I still always work on it in the studio- those are the best pieces to learn from: I've got nothing to lose since I'm going to throw  it out anyway, and I'm more willing to take chances and experiment. "The End of Ski Season" underwent some radical changes in the studio: I lightened the background mountain, added some variety to the greens in the foreground trees, and re-designed the snow patches on the ground plane.