After Yom Kippur, because all sins are attributable to the persuasive tactics of the yetzer. It convinces a person to believe the false doctrine of: "כוחי ועוצם ידי"—that all of my success and good accomplishments were due to my own powers, skills, and efforts. As it is written (Devarim 8, 11): "השמר לך פן תשכח את ה' אלקיך לבלתי שמר מצותיו... פן תאכל ושבעת ובתים טובים תבנה וישבת, ובקרך וצאנך ירביון וכסף וזהב ירבה לך וכל אשר לך ירבה, ורם לבבך ושכחת את ה' אלקיך המוציאך מארץ מצרים מבית עבדים... ואמרת בלבבך כוחי ועוצם ידי עשה לי את החיל הזה, וזכרת את ה' אלקיך כי הוא הנותן לך כח לעשות חיל". “Take care lest you forget Hashem, your G-d, by not observing His mitzvos . . . lest you eat and be satisfied, and you build good houses and settle, and your cattle and sheep increase, and you increase silver and gold for yourselves, and everything that you have will increase—and your heart will become haughty and you will forget Hashem, your G-d, Who took you out of the land of Egypt from the house of slavery . . . And you may say in your heart, ‘My strength and the might of my hand made me all this wealth!’ Then you shall remember Hashem, your G-d, that it was He Who gave you strength to make wealth.”
Sitting in the security of one’s house, beneath a solid roof, a person is liable to feel and believe in the false, delusive reality, chas v’shalom, of "כוחי ועוצם ידי עשה לי את החיל הזה". Therefore, HKB”H commanded us to vacate those premises and dwell in the tentative shade of the succah, beneath the vault of heaven. This is meant to instill in our hearts the understanding that we are living in Olam HaZeh under the governance of HKB”H. In other words: “You shall remember Hashem, your G-d, that it was He Who gave you strength to make wealth.”
Then, after accomplishing this tikun during the seven days of Succos—which represent the seventy years of a human lifespan in Olam HaZeh—HKB”H gives us a special day—Shemini Atzeres. We return to our homes infused with the brilliant, illuminating light of the mitzvah of succah. Thus, we remember even there that all of Olam HaZeh is nothing more than a temporary dwelling place, and we will be cautious not to be swayed by the yetzer hara to adopt the false conviction of "כוחי ועוצם ידי".
This explains fantastically the teaching in the Zohar hakadosh (Tzav 32a) that on Shemini Atzeres, HKB”H sits alone with Yisrael. Every person may request whatever he wants for the entire year, and HKB”H will grant his request. Here is the actual language of the Zohar:
ָהִִיב לֵֵיהּ."י וְְלֵָעֵֵי שָָׁאִִיב דְְּהִ מַַלֵיהּ, כְָָּחוֹדֵֵלִֵ לֵֵיהּ בִּלֵטַַ וְְנָָאִכְָָּלֵם מִַַעֵב ָתִִיין דְְּאִ"וּמַַ
Let us elaborate. On Chag HaSuccos, we are inculcated with the understanding and awareness that Olam HaZeh is merely a temporary dwelling; it is the passageway preparing us and enabling us to enter the banquet hall of Olam HaBa. Upon returning to our homes secure with this essential knowledge, we are entitled to request of HKB”H anything that we want, since there is no longer any risk of being enticed by the yetzer’s misleading suggestion of "כוחי ועוצם ידי". Instead, we take care to use all matters of Olam HaZeh exclusively for the sake of Hashem.
In this merit, we will be privileged to receive all the good that Olam HaZeh has to offer, so that we may use it for matters pertaining to Olam HaBa. Thus, we will successfully consolidate the name י"ה and fulfill the words of the passuk: "ואנחנו נברך י"ה מעתה ועד עולם הללויה"—but we will bless י"ה from now and forever, Halleluyah!
