Dr. Gerald Lambeau is a well-rounded character, but it's also clear what his main focus in life is: success and prestige. He's all about brains over brawn, brains over love, brains over friendship, brains over… well, basically over everything.
And it's this focus that often puts Lambeau into conflict with Sean Maguire. After all, Lambeau hired Maguire to help keep Will Hunting out of fights so he could focus on mathematics. But he's not happy when Maguire goes as far as asking Will to decide on his own version of success. As Lambeau bluntly tells Maguire, "Don't infect him with the idea that it's okay to quit, that it's okay to be a failure because it's not okay."
In other words, Lambeau will not be satisfied if Will chooses any path other than the one he (Lambeau) chose for himself.
In a sense, Lambeau is a good person who's just blind to seeing the world on any terms other than his own. When he speaks to Maguire, for example, he says,
LAMBEAU: You resent me. But I'm not going to apologize for any... any success I've had.
The truth is that Maguire is probably happy with the life he's chosen, but Lambeau can only see him as a failure who has squandered his abilities. For him, the good life means using your potential to achieve success, fame, and admiration from the people around you. And that's that.
Lambeau doesn't do a lot of growing by the end of this movie. But he does get upset enough to admit to Will,
LAMBEAU: Most days I wish I never met you. Because then I could sleep at night, and I wouldn't... and I wouldn't have to walk around with the knowledge that there's someone like you out there, and I didn't have to watch you throw it all away.
This comment helps us sympathize with Lambeau because it reminds us that his worldview can often cause him a lot of pain, especially when he's faced with someone as gifted as Will.
Lambeau can't stand the idea of Will throwing away his gifts because the truth is that Will could probably achieve more in one month than Lambeau has in his entire career. We don't know how things work out in the end for Lambeau, but we can probably assume that he'll not be happy with Will's decision to take off for California instead of working for a prestigious think tank.