Nīrakṣīra viveka nyāyaḥ (discerning milk mixed with water)
A swan has a God-given ability to extract and drink just milk from the mixture of milk and water.
This instruction is of great practical moral and spiritual value. On a materialistic level this is a way how to be not morose, but happy, and liked. Nīti-darpaṇa 1.16 states:
viṣād apy amṛtaṁ grāhyam amedhyād api kāñcanam nīcād apy uttamāṁ vidyāṁ strī-ratnaṁ duṣkulād api
A wise man will extract nectar from the pot of poison, takes a piece of gold from filthy place, accepts high advice even from a low man, and accepts chaste wife even from unworthy family. Such a moral man is looking for that what has some value in the worthless world. Naturally, such noble man will look for good qualities in others who otherwise might by looked upon. The ultimate valued object in a perception of this troublesome world is the spirit soul present individually in each and every living entity, not only in humans, but also aquatics, insects, beasts, plants. The high end is the appreciation of the Supreme Soul. On such a level of transcendental taste, there is no trouble, only pleasant spiritual atmosphere even in the midst of turmoil, at least for those, who are trained to see that way.