How we cite our quotes: All quotations are from The Graduate.
Quote #4
MR. MCGUIRE: I want to say one word to you. Just one word.
BENJAMIN: Yes, sir.
MR. MCGUIRE: Are you listening?
BENJAMIN: Yes, I am.
MR. MCGUIRE: Plastics.
BENJAMIN: Exactly how do you mean?
MR. MCGUIRE: There's a great future in plastics. Think about it. Will you think about it?
This is supposed to sound like soulless advice—at least, that's how Benjamin receives it. Mr. McGuire enters the picture to give us an idea about exactly who Ben doesn't want to be. Just think—he could have been on the cutting edge of 3-D printing by now. But it's a huge turn-off for Benjamin. He can't see himself in that world.
Quote #5
MR. ROBINSON: So I hope you won't mind my giving you a friendly piece of advice.
BENJAMIN: I'd like to hear it.
MR. ROBINSON: Ben, I think…I think you ought to be taking it a little easier right now than you seem to. Sow a few wild oats. Take things as they come. Have a good time with the girls and so forth.
Mr. Robinson is correctly diagnosing the fact that Benjamin is pretty anxious about his future. Ben ends up taking this advice in a way that Mr. Robinson would not be happy with at all (having an affair with his wife). He tries on the identity of "cool young man who has an affair with an older woman." It doesn't help. There used to be the idea that sowing one's wild oats was a necessary step in the process of becoming an adult.
Quote #6
BENJAMIN: Because I'm interested, Mrs. Robinson. Now what was your major subject at college?
MRS. ROBINSON: Art.
BENJAMIN: Art?
BENJAMIN: But I thought you…I guess you kind of lost interest in it over the years, then.
MRS. ROBINSON: Kind of.
Mrs. Robinson has just told Ben she doesn't know anything about art, and now he finds out it was her college major. She never got to develop her identity as an artist; her unplanned pregnancy and loveless marriage disrupted her life.
Mike Nichols described Mrs. Robinson to Anne Bancroft as someone who was angry with herself for giving up who she really was for wealth and security. She said she remembered this as she was filming this scene. (Source) Benjamin doesn't want to follow her example. But he already has, in a way—whatever he studied in college means nothing to him at this point, and he didn't come out of school with a sense of who he is and what he wants to be. His reasons are different, but the result's the same.