Restraint is insufficient in overcoming defilements. One needs to develop understanding as well.
Very good point, but that does not say that it is possible to understand it well if there is still no restain and somehow it also does not indicate that it would be easier if doing it without restain. It just tells that one who restains does not indicate that he has overcome lust.
That is a very importand thing as many believe that for instance a monk or ascet is a holy being forgetting that he could be a mine of lust.
a story from Abhidhamma in daily life:
2. Pariyutthana Moha
When moha arises together with the mind it is said that the bad mind, the unwholesome one; has appeared. Because of the concealing nature of this pariyutthana moha, evil consequences, which one may suffer in future, are not understood. And the evil of unwholesome actions of the present are also not understood. Therefore, even the learned and virtuous cannot see the evils of moha and will commit wrong deeds when moha arises. This moha in the domain of evils is the most wicked. In this world all wickedness and stupidity originate from moha; moha is the taproot of all evil.
The Wise Overwhelmed by Delusion
The Bodhisattva, Haritaca by name, having renounced the world, abandoning his immense wealth of eight crores of money became a hermit and attained the great supernatural power (jhana-abhinna). Then, as the rains were heavy in the Himalayas, he came to Baranasi and stayed in the King's garden. The King of Baranasi was his old friend who was fulfilling perfections parami to become the Venerable Ánanda. Therefore, as soon as he saw the hermit, he revered him so much that he asked him to stay in the royal garden and supported him with four requisites; he himself used to offer the hermit morning meals at the palace.
Once, a rebellion broke out in the country, the King himself had to go out to quell it. Before setting out with his army, he requested the queen again and again not to forget to look after the hermit. The queen did as told. One early morning, she took a bath with scented water and put on fine cloths and lay down on the couch awaiting for the hermit.
The Bodhisattva came through space with his supernormal power (abhinna), and arrived at the palace window. Hearing the flutter of the hermit's robe, the queen hastily rose from her cough and her dress fell off her. Seeing the naked queen, the anusaya moha which lay dormant in his mind-continuum, rose to the stage of pariyutthana moha, and filled with lust, he took the queen's hand and committed immoral transgression like a monster ogre.
We should consider the stupidity arising through moha in this story seriously. If such moha did not appear in him, he would not have committed such as evil deed even with the King's consent. But at the time, being overwhelmed by the darkness of delusion, he was unable to see evils of deed in the present and in future existences through out samsara, and consequently committed that improper transgression. The jhana-abhinna, which he acquired through practice for all his life, was unable to dispel the darkness of moha; instead, being overwhelmed by moha the jhana-abhinna powers themselves vanished from him.
But the hermit, being already quite matured in the perfection parami, learnt a bitter lesson and greatly repented his deed on the return of the King. He endeavored again and again his jhana-abhinna and contemplating, "I have done wrong because of dwelling in close proximity with the people," return to the Himalayas.
Note also, that Bodhisatta does not indicate "noble".
We actually do not train to be virtuos, but we train us in being virtouse to overcome moha.