The professor offered his guests hot chocolate in various cups, from plain to expensive. When the nice cups were all taken, leaving the plain ones, the professor used this as an analogy to explain that the cup holds the hot chocolate but does not change its quality or their enjoyment of it. Just as the cup is simply a vessel for the hot chocolate, their jobs and positions are the vessels for their life but do not define the quality of life they experience. They should focus on enjoying the life that God provides rather than concentrating only on the external factors like the cup.