What does Chapter 17 say about the true purpose of human life and the difficulty in achieving it?

According to Chapter 17, the true purpose of human life, or Purushartha, is to discard the path of Preya (the pleasant) and honor the path of Shreya (the good). This choice is likened to a swan separating milk from water. However, the text emphasizes that making this choice is difficult. Even when a person understands both paths and the choice is within their control, a dull-witted person without discrimination is often conquered by Preya and embraces it. The chapter encourages one to struggle for the sake of Shreya by strengthening the intellect, as this is where true human effort stands firm.