A beginner of golf seeks a coach yet needing another coach to learn other techniques. If one says one thing and the other coach says another, as a beginner, it would be very confusing because each teacher has their own ways and methods. Obviously the coach to seek for would be someone of professional status and has known much skills and knowledge. He would know much more than us already. If one seeks another shows the person is questioning the ability of the coach.
In any case, only if the teacher fails to give more than what the person can learn, then it's only fair to seek another more qualified teacher to teach something more advance.
On the spiritual side, if one is so fortunate to meet an esteemed lama to be your spiritual guide, there is really no need to seek another for one should think of the teacher as a Buddha. One should also be loyal to one's guru and shows respect even when one has gained Enlightenment as stated in the 50 Stanzas of Guru Devotion.
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As a disciple you must regard your Guru as an Enlightened Being. Even if from his own point of view he is not Enlightened and you, his disciple, have gained Buddhahood before him, you must still show him respect and pay homage. For instance, Maitreya, the fifth and next Buddha of the thousand of this world age, who now presides over Tusita Buddha-field, became Enlightened before his Guru, Sakyamuni Buddha. To demonstrate respect for his Guru, Maitreya has a stupa or reliquary monument on his forehead. Likewise Avalokitesvara, the incarnation of the compassion of all the Buddhas, is crowned in his eleven-headed aspect with the head of his Guru, Amitabha Buddha, the one who presides over Sukhavati Buddha-field.
This learning from a Guru should not be like killing a deer to extract its musk and then discarding its corpse. Even after attaining Enlightenment you must still continue to honor your Guru who made all your achievements possible.
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What is more to say if one is to run from one master to another?