(7) Adonai formed (va'yitser, root word יצר) the human of the dust of the ground, and breathed into his nostrils the breath of life; and the human became a living soul.
(ה) וַיַּ֣רְא ה' כִּ֥י רַבָּ֛ה רָעַ֥ת הָאָדָ֖ם בָּאָ֑רֶץ וְכָל־יֵ֙צֶר֙ מַחְשְׁבֹ֣ת לִבּ֔וֹ רַ֥ק רַ֖ע כָּל־הַיּֽוֹם׃ (ו) וַיִּנָּ֣חֶם ה' כִּֽי־עָשָׂ֥ה אֶת־הָֽאָדָ֖ם בָּאָ֑רֶץ וַיִּתְעַצֵּ֖ב אֶל־לִבּֽוֹ׃ (ז) וַיֹּ֣אמֶר ה' אֶמְחֶ֨ה אֶת־הָאָדָ֤ם אֲשֶׁר־בָּרָ֙אתִי֙ מֵעַל֙ פְּנֵ֣י הָֽאֲדָמָ֔ה מֵֽאָדָם֙ עַד־בְּהֵמָ֔ה עַד־רֶ֖מֶשׂ וְעַד־ע֣וֹף הַשָּׁמָ֑יִם כִּ֥י נִחַ֖מְתִּי כִּ֥י עֲשִׂיתִֽם׃
(5) And Hashem saw that the evil of the human was great in the earth, and that every yetser of the thoughts of the human heart was only evil all day. (6) And Hashem regretted having created the human on the earth, and it grieved Him at His heart. (7) And Hashem said: ‘I will blot out the human that I have created from the face of the earth; from human to beast to creeping thing to fowl of the air; for I regret that I have made them.’
(21) And Adonai smelled the sweet smell; and Adonai said in His heart: ‘I will not again curse the ground for humanity’s sake; for the yetser of a person's heart is evil from his youth; I will not again smite every living thing, as I have done.
(5) I am the LORD and there is none else; Beside Me, there is no god. I engird you, though you have not known Me, (6) So that they may know, from east to west, That there is none but Me. I am the LORD and there is none else, (7) I form light and create darkness, I make shalom and create ra — I the LORD do all these things.
(א) "מנעריו" - מנעריו כתיב משננער לצאת ממעי אמו נתן בו יצר הרע
"From his youth" It says from his youth, (m'n'urayv, root word נער) from when he shook (n'na'er, root word נער) to come out of his mother's innards, the yetser ha'ra was given in him.
אמר רב יצחק יצרו של אדם מתחדש עליו בכל יום שנאמר (בראשית ו, ה) רק רע כל היום ואמר ר"ש בן לוי יצרו של אדם מתגבר עליו בכל יום ומבקש המיתו שנאמר (תהלים לז, לב) צופה רשע לצדיק ומבקש להמיתו ואלמלא הקב"ה עוזרו אין יכול לו שנאמר אלהים לא יעזבנו בידו
Rabbi Yitshak said a person's yetser renews upon him every day, as it is written "only evil all day." And Rabbi Shimon the son of Levi said a person's yetser overcomes him every day and seeks to kill him, and if it were not for the Holy One's help a person could not withstand it.
(ז) רבי נחמן בר שמואל בר נחמן בשם רב שמואל בר נחמן אמר: הנה טוב מאד, זה יצר טוב. והנה טוב מאד, זה יצר רע. וכי יצר הרע טוב מאד אתמהא?! אלא שאלולי יצר הרע, לא בנה אדם בית, ולא נשא אשה, ולא הוליד, ולא נשא ונתן. וכן שלמה אומר: (קהלת ד): כי היא קנאת איש מרעהו:
(7) Rabbi Nahman said in Rabbi Samuel's name: 'Behold, it was very good' refers to the yetser ha'tov (the good yetser) 'And behold, it was very good' refers to the yetser ha'ra. Can then the yetser ha'ra be very good? That would be extraordinary! But without the yetser ha'ra no man would build a house, or take a wife or beget children, or give and take (engage in business). As Solomon said: "Again, I considered all labour and every skill in work, that it comes from a person's rivalry with his neighbor." (Ecclesiastes 4:4).
אותיבו בתעניתא תלתא יומין ותלתא לילואתא מסרוהו ניהליהו נפק אתא כי גוריא דנורא מבית קדשי הקדשים ... אמר להו חזו דאי קטליתו ליה לההוא כליא עלמא חבשוהו תלתא יומי ובעו ביעתא בת יומא בכל ארץ ישראל ולא אשתכח אמרי היכי נעביד נקטליה כליא עלמא ניבעי רחמי אפלגא פלגא ברקיעא לא יהבי כחלינהו לעיניה ושבקוהו ואהני דלא מיגרי ביה לאיניש בקריבתה
Talmud Bavli, Yoma 69b
They (The Ancient Sages) ordered a fast of three days and three nights, whereupon he (The Yetzer HaRa) was surrendered to them. He came forth from the Holy of Holies like a young fiery lion. He (one of the rabbis) said to them: Realize that if you kill him, the world goes down. They imprisoned him for three days, then looked in the whole land of Israel for a fresh egg and could not find it. Thereupon they said: What shall we do now? Shall we kill him? The world would then go down. Shall we beg for half-mercy? They do not grant ‘halves’ in heaven. They put out his eyes and let him go. It helped inasmuch as he no more entices men to commit incest.
(א). . . והמלאכים עובדים את בוראם ואין להם יצר הרע, והבהמות יש להם יצר הרע ואין להם דעת. וממילא דלהמלאכים אינו מגיע שכר בעד עבודתם, אחרי שאין להם יצר הרע, ולבהמות לא שייך עונש אחרי שאין להם דעת. (ב) ולזה ברא הקדוש ברוך הוא ביום הששי את האדם. ובראו משני הקצוות: נתן בו את הנשמה שמאירה לאדם לדעת את הבורא יתברך כמלאך, כמו שנאמר: "כי נר ה' נשמת אדם". ויצר אותו בגוף שהוא חומר עב כבהמה, לאכול ולשתות ולישן. ולזה יתעוררו מלחמות גדולות בהאדם כל ימי חייו, שהנפש הבהמי מסיתו לתאוות עולם הזה כבהמה, והנשמה הטהורה נלחמת כנגדו ומראה לו שלא לכך נברא אלא לעבוד את הבורא כמלאך. ואף הדברים הגשמיים שמוכרח לעשות כאכילה ושתייה ושינה – תהיה הכוונה כדי שיוכל לעבוד את בוראו.
(1) Angels serve their Creator, and do not have yetser ha'ra. Animals, on the other hand, have yetser ha'ra but lack intelligence. The result is that angels cannot receive reward for their service, as they have no yetser ha'ra to overcome, and animals cannot be punished for their actions, as they do not have the intelligence. (2) Therefore G-d found it necessary to create the human on the sixth day, and God created the human from both sides: God gave him a spiritual soul that enables him to recognize the Creator as does an angel, as the verse states: “God's candle is the human soul…” (Mishlei 27:20). And God created him in a body which is thick material, like a beast, to eat and drink and sleep. As a result, a great battles wage within a person all his days. His animal spirit incites him to desire this world like an animal, and the pure soul battles against him and shows him that he was not born for this, but to serve the Creator like an angel. And even physical things that one must do, like eating and drinking and sleeping -- should be done so as to to serve God.
כי פנימיות הכל כח הבורא ית' והוא אמת. רק שיש שפה וקליפה מבחוץ והוא ציור ודמיון ונק' יצר הרע.
Sefat Emeth, Shabbat Chanukah, 5640
For the core of everything is the power of the Blessed Creator, which is truth. But there is language and shell on the outside, and that is just depiction and imagination, and it is called yetser ha'ra.
והתניא ר"ש בן אלעזר אומר משום חילפא בר אגרא שאמר משום ר' יוחנן בן נורי המקרע בגדיו בחמתו והמשבר כליו בחמתו והמפזר מעותיו בחמתו יהא בעיניך כעובד ע"ז שכך אומנתו של יצה"ר היום אומר לו עשה כך ולמחר אומר לו עשה כך עד שאומר לו עבוד ע"ז והולך ועובד א"ר אבין מאי קראה (תהלים פא, י) לא יהיה בך אל זר ולא תשתחוה לאל נכר איזהו אל זר שיש בגופו של אדם הוי אומר זה יצר הרע
One who tears his clothing in anger and one who breaks his dishes in anger and one who scatters his money in anger will be in your eyes like one who worships idolatry. For so is the craft of the yetser ha'ra. Today he says to him "do such", and tomorrow he says to him "do such", until eventually he says to him "worship idolatry", and the person goes and worships. Rabbi Abin says, what does Psalms mean when it says "You should not have a strange God in you and should not bow to a foreign God?" What strange God does a person have in his body? We can say that this is yetser ha'ra.
Rabbi David Jaffe, Changing the World from the Inside Out
A literal translation of yetzer harah is "evil/bad inclination" although the "evil/bad" part is not exactly accurate because it is a morally neutral force. It is simply the drive for instant gratification. Depending on how we direct this drive, it can build and create or tear down and destroy.
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In Jewish sources the yetzer harah lives in tension with the yetzer tov, the "good inclination." The yetzer tov functions in a similar way to what neuroscientists call the "prefrontal cortex," the part of the brain that weighs priorities, makes decisions, and engages in rational thought. Again, "good" is a bit of a misnomer because too much yetzer tov can also be destructive. The ideal is a balance where both inclinations work together toward prosocial goals. Achieving such a balance is the art of living well. If the yetzer harah is all about "me," the yetzer tov is other focused and puts the "me" in a context of relationships and the world at large. The yetzer harah is like a single wall of an A-frame. Since it is only concerned with "me," it has nothing to lean against and falls over easily. By bringing the "me" into relationship, the yetzer tov helps create something sustainable.