SB 9.10.27

na vai veda mahā-bhāga
 bhavān kāma-vaśaṁ gataḥ
tejo ’nubhāvaṁ sītāyā
 yena nīto daśām imām
Synonyms: 
na — not; vai — indeed; veda — did know; mahā-bhāga — O greatly fortunate one; bhavān — yourself; kāma-vaśam — influenced by lusty desires; gataḥ — having become; tejaḥ — by influence; anubhāvam — as a result of such influence; sītāyāḥ — of mother Sītā; yena — by which; nītaḥ — brought into; daśām — condition; imām — like this (destruction).
Translation: 
O greatly fortunate one, you came under the influence of lusty desires, and therefore you could not understand the influence of mother Sītā. Now, because of her curse, you have been reduced to this state, having been killed by Lord Rāmacandra.
Purport: 

Not only was mother Sītā powerful, but any woman who follows in the footsteps of mother Sītā can also become similarly powerful. There are many instances of this in the history of Vedic literature. Whenever we find a description of ideal chaste women, mother Sītā is among them. Mandodarī, the wife of Rāvaṇa, was also very chaste. Similarly, Draupadī was one of five exalted chaste women. As a man must follow great personalities like Brahmā and Nārada, a woman must follow the path of such ideal women as Sītā, Mandodarī and Draupadī. By staying chaste and faithful to her husband, a woman enriches herself with supernatural power. It is a moral principle that one should not be influenced by lusty desires for another’s wife. Mātṛvat para-dāreṣu: an intelligent person must look upon another’s wife as being like his mother. This is a moral injunction from Cāṇakya-śloka (10).

mātṛvat para-dāreṣu
 para-dravyeṣu loṣṭravat
ātmavat sarva-bhūteṣu
 yaḥ paśyati sa paṇḍitaḥ

“One who considers another’s wife as his mother, another’s possessions as a lump of dirt and treats all other living beings as he would himself, is considered to be learned.” Thus Rāvaṇa was condemned not only by Lord Rāmacandra but even by his own wife, Mandodarī. Because she was a chaste woman, she knew the power of another chaste woman, especially such a wife as mother Sītādevī.