Jacob did not understand the culture, customs, and nature of Contracts or Covenants in Haran. From his entrance into the region Jacob was introduced to a different way of life, but maintained his way of doing things.
Jacob makes a covenant or verbal contractual agreement with Laban not fully understanding the firstborn sister marriage-first custom. Laban knew this going into the agreement, but neglected to tell Jacob the small print. Leah was in on the misrepresentation because she would have to lay with Jacob and it was clear for seven years that Jacob was working for Laban in order to marry her sister, Rachel.
We see that in this culture the daughters did what was instructed by their fathers, who chose whom their daughters would marry. Rachel was in on the plan too. She knew there was a marriage feast and that Jacob would be wed to Leah, but Rachel kept quiet. Jacob had to accept the arrangement for he had no choice if he wanted Rachel.