Devar Eliyahu (2 ¹ ): He cursed the Mazal of the day of his birth, and the night of his conception ² . He thought that everything depends on Mazal. He knew that he was born during the day, or he assumed so, for most births are during the day.

Malbim: Some people think that the Ma'arachah influences only who is apt to receive Chochmah or Nevu'ah, but not wealth, marrying many women, love or hatred. Astrologers say that the Ma'arachah influences all of these. They can predict his lifespan, and if he will father children. The Chachamim who said that Mazal makes wise or rich (Shabbos 156) hold like this. Iyov held like this. This is why he cursed the night of his conception and the day of his birth, for Mazal determines whether or not one will succeed. Hashem knows everything, but He is not to blame, for the Ma'arachah determines everything; man has no choice.