Why did reuben lose his first-born blessing?

Reuben lost his first-born blessing due to his actions, specifically when he slept with Bilhah, his father's concubine. This act was seen as a severe violation of family honor and authority, leading Jacob, their father, to revoke Reuben's birthright. Consequently, Jacob declared that the blessings of the firstborn would be given to Joseph and his sons instead. Reuben's impulsive behavior and failure to uphold his familial responsibilities ultimately cost him this significant privilege.