The Foxes were defeated 3-1 by the Seagulls and were 2-0 down at half time.
Despite pulling a goal back through Andy King, Leicester conceded a third with 13 minutes remaining and were unable to find a way back into the game.
"I didn't think we showed the desire, the energy levels or the drive to go out and do the job," Pearson told the club's official website.
"People will say we were complacent and I can't argue with that. We were poor in the first half and we gave two poor goals away. They were avoidable."
Leicester are now third in the Championship, one point behind leaders Burnley.