Here we see too the necessity of the Yetser HoRo for physical survival. Like a butterfly that bursts forth from its chrysalis, its effort to exit providing it with the necessary strength to develop its wings, to thrive and fly forth, so the struggle to live and battle against adversity, is the raison d'être, the energy and essence of the Yetser HoRo, providing the Neshomoh incarnate with the necessary wherewithal to flourish in the physical world.
Thus the Yetser HoRo is not all evil. It is a requisite ingredient of man's existence, essential for his survival. But like all ingredients, it needs to be tempered and controlled, applied in the correct measure. "Man only transgresses if a spirit of folly enters him," say our sages. This foolishness can only take hold if the narcissistic nature of the Yetser HoRo gains the upper hand and the other ingredients of the psyche become subservient to it, thus poisoning an otherwise very palatable dish.
Amazingly, the Arizal says that the Yetser HoRo is the outer protective layer of the Yetser HaTov, its husk. Like peel surrounding a fruit, the Yetser HoRo protects the Yetser HaTov.
Thus, the Yetser HoRo, though associated with the feelings, memories, and urges of the body (see fig. 4), is ultimately here to serve the Yetser HaTov. If a person conducts himself properly, making the right moral choices and fulfilling G-d's Will, the Yetser HoRo will help the Yetser HaTov, strengthening and adding its own brand of zest to the Yetser HaTov's energy.
Both the Yetser HaTov and the Yetser HoRo are here to protect and help us in this world. Angelic forces, their purpose is to care for the Divine soul and to assist it in its work within the physical. Like salt preserves meat, the Yetser HoRo preserves and protects the living organism. It is a force created by the soul's will to be and helps him survive within the material plane.
It is only when this force goes overboard, when the will to express the self contradicts the divine soul's inherent moral instinct, that it takes the form of egotistical or crass behavioural conduct most commonly associated with the Yetser HoRo.
From the verse יצר מחשבות לבו, "the products of the thoughts of his heart," it appears that the yetser is bound with the thoughts and imagery of the heart and mind. "Products of the thoughts of his heart" are the material used by the two yetsers. Both yetsers compete to influence the mind with emotive imagery of ideas and concepts, the thinking Chochmoh mind through the imaginative Binoh (see next chapter for this definition of Chochmoh and Binoh), though the yetser horo tends more towards the emotions and the yetser tov to the intellect.
Thus we may counteract or transform the Yetser HoRo ("evil" inclination) by using positive imagery.
Since the subconscious does not differentiate between factual memory and what is imagined, we can generate positive behaviour by feeding the subconscious with positive imagery. Moreover, as mentioned earlier, thought has a concrete effect in the higher realms, which must subsequently affect the lower energy-manifestations. Thus, a most effective way to overcome the Yetser HoRo is by consciously imagining good behaviour, seeing yourself in that mode, imagining and enjoying the experience. This meditation method is advocated by Rabbi Yisroel Salanter and is a by-product of the "service of the heart" that is Tefilloh – prayer.
 This truth has recently been echoed by the modern psychologist and writer, Mihaly Csikszentmihalyi: "Attention is like energy... We create ourselves by how we invest this energy. Memories, thoughts and feelings are all shaped by how we use it. And it is an energy under our control, to do with it as we please...." (Flow: The Psychology of Optimal Experience, p.33 - NY. Harper Perennial Modern Classics. 1990.)). His words are predated by a comment by Rabbi Nachman of Breslav, who, over two hundred years ago, recorded in his magnum opus, Liqutei MoHaRan (2:50) "Thought (i.e. where a person places his attention) is under man's control, to incline it to wheresoever he wishes...."
 Thus the Rabbis say לעולם ירגיז אדם יצר טוב על יצר הרע – A person should always "excite" his good inclination over the evil inclination; i.e. positive thoughts, meditations, etc., the effort wrought to keep the attention focused correctly, strengthens the Yetser HaTov.
 Soteh 3a, Zohar Vol. I, 121a
 See Tanchumoh, Bereishis, 7 - "G-d says: 'You made it [the Yetser HoRo] evil'…"
 The comparing of the Yetser HoRo to the peel surrounding a fruit indicates that the Yetser HoRo is, in essence, an outgrowth – the husks - of the naturally spiritual urges of the Yetser Ha-Tov.
 Interestingly, the English word "evil" has the same letters as "live."
 In parenthesis, we can now appreciate what happens to the two yetsers as a person matures, as explained by the sages. Until age twelve/thirteen, the brain cannot fully process idealistic or altruistic ideas, thus the Yetser Ha-Tov, which works primarily through ideas, is somewhat weak. Moreover, the boundary between the conscious and subconscious (the Conscious Critical Faculty discussed later) is not properly formed; hence, a child is in a constant state of semi-trance, open to suggestions and influences, his behaviour veers to the egotistical, the outcome of a fertile mind recording and readjusting, ingraining habits, reactions and animalistic responses based on the senses' experiences and the heart/mind imagery i.e. the subconscious. Because the Inner Mind is still in the process of "settling" within the physical and has yet to start properly interacting with the conscious, and the guardian/filter to the subconscious mind (the CCF) is not sufficiently developed, choices will be strongly influenced by the physical senses and by paternal authority; thus, the sages say, till he becomes a Bar-Mitsvah, he has only the Yetser HoRo. Furthermore, each time he enacts his inclination, he creates and enlarges upon the energy of the Yetser HoRo. (The converse is equally true. Every correct choice creates "good" angelic energy, which energy enlarges the Yetser Ha-Tov. The Yetser HoRo is strengthened by sin and the Yetser Ha-Tov by Mitsvos.)
 Perhaps better translated as "a derivative of Ro", whatever רע "ro" means; see note 230.