JUDGE: It's now your duty to sit down and try and separate the facts from the fancy.
Just before the jurors retreat to their jury room, the judge reminds them that they have a very important responsibility to get past their versions of reality and to come up with the version that makes most sense. That's the whole point of having twelve jurors instead of one, since twelve jurors are more likely to come to a more objective version of reality.
JUROR #10: Look, we're all grown-ups in here. We heard the facts didn't we? You're not gonna tell me we're supposed to believe this kid, knowing what he is.
We can tell early on that Juror #10 has a strong bias against the defendant because the defendant is non-white. This claim also shows us that rather than being totally objective, this juror is more than willing to indulge his petty racism, even if it ends up getting the defendant electrocuted.
JUROR #3: Here's what I think. And I have no personal feelings about this. I just wanna talk about facts.
We know that the whole "I have no personal feelings" is a bunch of hooey, since it's impossible for any one person to claim they're totally objective about something. Juror #3 says he just wants to talk about facts, but we learn at the end of the movie that he's the most biased juror out of the entire bunch.
JUROR #3: Now these are the facts. You can't refute facts. The kid is guilty. I'm just as sentimental as the next fella. I know he's only 18.
Juror #3 continues to talk about facts as a way of hiding his prejudice. He claims that he has sympathy for the kid who's on trial for murder, but we know that this guy has a lot of personal hang-ups about sons not respecting their fathers, and he's perfectly willing to send the kid to the electric chair as a result.
JUROR #10: He's twisting the facts. Did or didn't the old man see the kid running out of the house at 12:10?
When Juror #8 calls into question whether one of the murder witnesses (an old man) saw the defendant running away from the crime scene, Juror #10 gets really angry and accuses #8 of twisting the facts. But that's just the thing: if facts can be twisted, then how reliable are they?
JUROR #3: What are you talkin' about? I mean, we're all going crazy in here or something.
Like Juror #10, Juror #3 can't believe it when he sees the room starting to turn toward a "Not Guilty" verdict. He assumes that everyone around him is going crazy. After all, there are some people who just aren't all that good at changing their minds about something once they've decided on it. And this can make their version of reality really rigid.
JUROR #3: What is this? Love Your Underprivileged Brother Week?
When he realizes that the room is turning against him, Juror #3 decides that the rest of the men are weak for letting their versions of reality be swayed so easily. He accuses them of being a bunch of bleeding hearts who don't have the guts to do what is right. But by the end of the movie, he's the one who's bawling his eyes out over his lost son.
JUROR #10: Well, don't you know about them? There's a… there's a danger here.
Even after most of the jury members have changed their minds, Juror #10 continues to insist that they should convict the defendant because he's a dangerous person of color. It's not until the entire room (literally) turns on him (even the people who agree with his verdict) that he finally shuts up and stops talking.
JUROR #9: No. He wouldn't really lie. But perhaps he made himself believe he heard those words and recognized the boy's face.
Out of all the jurors, Juror #9 seems to be the most open to the idea of different people seeing reality in different ways. For example, he thinks that the old man who apparently witnessed the defendant running from the crime scene might have just imagined he saw the boy's face and then, later on, convinced himself that he was right. It just goes to show how our minds can often warp what we think is real.
JUROR #8: You don't really mean you'll kill me, do you?
Midway through the movie, Juror #8 gets on Juror #3's nerves so much that Juror #3 says he'll kill him. But as Juror #8 reminds us, we say stuff like this all the time without meaning it. So we shouldn't always take the things we say literally, just like we shouldn't take it too seriously that the defendant told his dad he'd kill him a few hours before the old man died.