When the demonic king Ravana abducted Sita deceitfully from the Dandaka forest, Lord Rama and his younger brother Lakshman were moaning in grief. They wandered all around the forest in vain.
Seeing this, Lord Shiva who kept a close watch over earthly matters from Mount Kailash also started weeping.
His wife, Goddess Sati asked him the reason to cry after seeing a mere mortal weeping. Lord Shiva told her that the person she considers to be a mere mortal is actually the incarnation of Lord Vishnu.
Since Lord Rama was weeping upon the abduction of his wife thereby displaying human emotions, Sati could not digest the fact and therefore she decided to test whether Lord Ram was really the incarnation of the almighty God or not.
She transmuted herself to Goddess Sita and went to the dandaka forest where Lord Rama and Lakshman were searching for Goddess Sita.
She approached them in the form of Goddess Sita and thought that both the princes would not believe their eyes but as soon as she approached Lord Rama, instead of jumping out of joy and hugging her, he greeted her with a namaskar and asked about the whereabouts of her husband; Lord Shiva.
Goddess Sati could not believe this and out of utter shame returned to Mount kailash.