The Sikshavalli division of the Taittiriya Upanishad details what a teacher tells his student, when the latter has completed his period of study. The teacher tells his pupil never to utter a lie. Now what is the need for this specific instruction, the pupil may wonder. After all, as a student he has always shown regard to the truth. But the reason for the instruction is because the student is now stepping into worldly life. He has a future ahead of him, which will include marriage, a vocation and many responsibilities. The occasions to tell lies and temptation to tell lies will be many, because he no longer lives sheltered from the outside world, elaborated Velukkudi Krishnan, in a discourse. Sometimes to obtain something of absolute necessity to him, he may have to tell a lie. But in spite of all this, he should keep to the path of truth, and that is why the teacher tells him to speak the truth always.
However, there may be occasions when speaking the truth may harm or hurt someone. At such times, one must refrain from speaking the truth. A cow was being chased by a man, and the cow ran into the hermitage of a sage. The man who was chasing the cow came to the hermitage and asked the sage if he had seen a cow. The sage replied that he had not. In this case, had the sage spoken the truth, the cow would have been killed. So he did the right thing by lying. Sometimes, we may have to observe silence, because silence keeps us from telling a lie. Silence too is a form of truth in such instances.