In the story, Rama goes chasing a golden deer (which actually is the Rakshasa Maricha in disguise), and does not return for long. When Sita coerces Lakshmana to leave in search of his brother, Lakshmana who cannot bear to see Sita cry in grief, reluctantly decides to go and search for Rama, subject to his condition that Sita not cross the protective line he draws. Anybody other than Rama, Sita and himself attempting to cross the line would be singed by flames erupting from the line. Once Lakshmana leaves in search of Rama, the Rakshasa king Ravana comes in the form of a mendicant and asks Sita for alms. Not expecting a trick, she unsuspectingly crosses the Lakshman Rekha to provide alms to him and Ravana kidnaps her in his Pushpaka Vimana.
Radhey Shyam Ramayan mentions that the crossing of Lakshaman Rekha by Sita was done absent-mindedly by an anxious Sita only to honour the great Indian tradition of "अतिथि देवो भवः" (Atithi Devo Bhava): the guest is embodiment of a Deva (divine entity). Sita crosses the boundary line only to give alms to Ravana once he insists that alms cannot be accepted across a barrier as having a boundary in between was against the principle of free will of the donor.