So every day I wove on the great loom, but every night by torchlight I unwove it; and so for three years I deceived the Akhaians.
This line shows that Penelope is clever because at the beginning of the passage, Penelope requests that the suitors leave her alone and not ask her to marry until she finishes weaving a death shroud she had already started because if she were not allowed to finish, her efforts at beginning the shroud would have been in vain. To this appeal to their emotions, the suitors agree. And, knowing the suitors would respect her request, at the end of a day of weaving, she would undo all she had done in the daytime thereby keeping the suitors at bay for 3 years.