It is said that if a pregnant woman is unhappy or stressed, then the foetus will be affected. It could not only have health problems, it could also have psychological problems later on. Sita was unhappy when She was pregnant. And yet, Lava and Kusa were not affected adversely by Her sorrow. They turned out to be intelligent, cheerful children. The reason for this was that Sita, although banished by Rama to the forest, had taken up residence in the ashram of Valmiki. And while there, She heard the Ramayana that Valmiki had composed. That must have contributed to the brilliance and equipoise of her children, said M.V. Anantapadmanabhachariar, elaborating on the need to pay heed to the words of gnanis.
Sage Vasishta was exceedingly unhappy, because all his hundred sons had been killed. He willed himself to live, only to see the birth of his grandchild. His son's Sakthi's wife was pregnant, and it was the birth of this grandhchild that the sage was looking forward to. One day he heard the child in the mother's womb reciting the Vedas, and he was astounded! The child must have absorbed what it was hearing around it, and since its grandfather Vasistha was a great sage himself, the child must have been exposed to the constant recitation of mantras and Vedic chants. Even so it was a rare feat for a foetus to be able to recite the mantras.
While mantras bring benefit to us, we must learn them from a proper guru. To try to learn them on our own is not proper. The guru we seek must be competent to teach us the mantras with proper pronunciation and intonations. Once a king told a learned man that he could recite the Vedas better than the learned man could. The scholar wanted to teach the king a lesson. So he shouted to the guards, “Arrest the king!” The king, taken aback by the man's audacity, ordered the guards to arrest the scholar, and the guards, immediately complied. The scholar thereupon said,” When I ordered them to arrest you, did they obey my command? But when you gave an order, they obeyed you. That is because you have the authority to command them, and I do not. Likewise, I am a scholar and you cannot be dismissive of me.” Thus we should learn mantras from those qualified to teach them, and we should not attempt self- instruction.