In ancient India the swan was revered because it reputedly has the power of separating milk from water. Therefore, wise men were called swans for their ability to discriminate that which is useful for spiritual growth from that which is not. This is a very important quality for the sAdhaka to cultivate early on. By doing so, the aspirant can take what is useful from every interaction in life. On the spiritual path one meets many self-styled teachers. For instance, your local yoga teacher may only be capable of teaching Asana yoga. While believing implicitly in a teacher of limited capability is not useful, so is outright rejecting the opportunity to learn something. By exercising discrimination you can learn that which is useful and leave the rest for another learning experience, or personal sAdhanA.
It is equally important to dispassionately leave behind that which is not useful in an interaction. What is not useful can be left behind without getting upset about it. There is a famous story about the Buddha who gently told a lady who was about to put some filth in his bhiksha bowl that "Mother, I don't need this". Being a yogi does not mean one has to take abuse.
One has to realize that all people are subject to the play of the three guNas: sattva, rajas and tamas. This is true even for close family members, including parents, children, and spouse. The sAdhaka should recognize that this is true even of teachers one encounters along the way, unless one is fortunate enough to meet a guNAtIta (one who has transcended the guNAs). This is very rare.
Whatever comes from sattva guNa is always worth taking. In time the sAdhaka can gain enough discrimination to even gain something useful from those who appear to be inimical. Often great insights of wisdom are hidden in the criticism that one might encounter in a difficult interaction. If buddhi--the discriminating, dispassionate, observing faculty of mind--is cultivated carefully, one can distance oneself from the initial reaction and learn from the criticism (if there is any truth in it). However, one should never condemn oneself for any reason because such an attitude is never useful. That which is past should be left behind, and one should make the best of the present moment, for in truth that is all that one has.
Since everyone is subject to the play of the three guNas, it is not surprising that one can learn something from almost anyone. However, the predominant guNa is different in different people. It is not useful to cultivate company that is excessively rAjasic or tAmasic, and as sAdhanA progresses such associations will naturally fall off. The practice of meditation allows one to observe the ahamkAra or ego aspect of one's mind clearly, and so it becomes easier to sift the constructive aspects of criticism. When eventually all useful lessons that can be learnt from life are learnt, then there is no stopping the sAdhaka's spiritual progress.
In the earlier stages the sAdhaka is encouraged to cultivate satsang, or the company of those in whom sattva guNa is predominant. In time the sAdhaka will develop an indifference even for sattva guNa, or in other words the yogi becomes indifferent to goodness for its own sake. Being sAttvic is by itself not liberating, but it is a pre-condition for gaining the Gnosis that liberates.
My mother used to recite a shloka by Adi ShankarAcArya that says:
satsangatve nissangatvam nissangatve nirmohatvam
nirmohatve nishcalatattvam nishcalatattve jIvanmuktih
From satsang to avoidance of company, from this avoidance of company to absence of illusion or ignorance
From absence of illusion or ignorance to Gnosis of the unchanging Essence, and from this Gnosis to liberation in life.
The discriminating characteristic of the swan should be borne in mind along this path of progression from one stage to the next.