For me, the section of this narrative that I feel has so much to teach is "Hair-Pinning Days," though of course all of the different sections are incredibly important. What is significant about this particular chapter in Lily's life is what she learns about her friend Snow Flower and the way in which she responds to it.
Let us remember that in this section, it becomes clear that Snow Flower's family has lost its wealth thanks to her father's opium addiction. Things have become so bad that Snow Flower is forced to marry a butcher, which represents a drop in social status. Lily therefore realises that the friendship that Madam Wang forged between her and Snow Flower was not an act of kindness, and that it was done specifically with the aim of saving Snow Flower's reputation through association. What I think we can learn from this situation is the way that Lily responds. She obviously feels hurt by how she has been deceived, but at the same time, she sees that Snow Flower was not responsible for it, and continues to accept and love Snow Flower as her friend rather than shun her because of the deception.
We therefore can learn an important lesson if ever we are manipulated and deceived by others, which is to make sure that we do not blame the wrong person for that deception, and also to not allow that deception to change our perspective of those who might have been innocently caught up in the lies.