The Tale of Chicholo

However, this wasn't a true A-class painting. It was awfully close to being one, yet it just missed a final bit… It was as if it was right on the edge, oh so close! It made Lin Ke a little regretful that this painting wasn't a true top-tier painting. 

Lin Ke looked at the painting deeply, trying to find the reason for that feeling. What was the thing that was missing? What was the final piece to this puzzle? What, if done when this painting was made, would have caused it to truly become a generational masterpiece?