Chapter 17 uses an analogy involving a swan. Can you explain this analogy and how it relates to choosing between Shreya and Preya?

In Chapter 17, the text presents a powerful analogy to illustrate the choice between Shreya (the Good) and Preya (the Pleasant). It states that just as a swan, or Maral, can miraculously separate and drink only the pure milk from a mixture of milk and water, a wise and courageous person can distinguish and cling only to Shreya. This analogy, as detailed in the chapter, highlights that even though Shreya and Preya are often blended in life, those with discrimination and intelligence can turn away from the worldly temptations of Preya and embrace the path of spiritual wisdom.