The Gemara (Rosh Hashanah 16:) states, "Three sefarim are opened [in heaven] on Rosh Hashanah. One sefer is of complete resha'im, one of complete tzaddikim, and one of beinanim (between tzaddikim and resha'im). The perfect tzaddikim are written and signed immediately for life. The complete resha'im are written and signed immediately for death. The beinonim wait from Rosh Hashanah until Yom Kippur. If they merit it, they will be written for life. Otherwise, they will be written for death."
Toldos Yaakov Yosef (Re'eh) explains that for this judgment, the key is to want to be a perfect tzaddik. The judgment isn't on the deeds, but where you want to be this year. If you want to be a perfect tzaddik, you will immediately be inscribed in the book of tzaddikim.
Reb Mordechai Chaim of Slonim zt'l repeated the following mashal each year at the seudah hamafsekes: Someone owned a beautiful bird, and people would pay money to see it. A thief stole the bird, but he didn’t know how to take care of it. The bird became skinny and weak. It was no longer worth keeping, so he brought it to the town's shochet. At least he would get a meal out of it. At the shochet's place, he met the true owner of the bird. "Give it back to me," the owner demanded. "It's my bird." The thief replied, "Your bird was fat and beautiful, and this bird is scrawny and bony. How can you claim this is your bird?" The shochet said, "I won't shecht the bird before the rav rules over the case and determines who is the owner of the bird." Three people arrived at the rav’s door: the shochet, the true owner, and the thief. The rav took the bird, untied the rope that bound its feet, and the bird ran to its true owner. Reb Mordechai Chaim explained, "Throughout the year, the yetzer hara makes it hard for us to serve Hashem. On Yom Kippur, Hashem takes the yetzer hara away. Now, let's see where you run to. If you run to Hashem, that shows that you belong to Him."
