ATMachine said:
The book also makes clear how much Lucas controlled things during shooting: he was always on set, and not infrequently offered the actors advice that was contradictory to that of the director. Marquand's personality didn't help: he seems to have been very meek and introverted, and never really bonded with many of the actors. In other words, a perfect hired gun.
Which brings up the question as to why he even hired Marquand if he was spending his time everyday on the actors anyway. In Empire, while he practically directed pre- and post-production himself, he at least let Kershner work with the actors instead of him, justifying his hire.