During the knife scene, Juror #8 states "It's possible!" while Juror #4 retorts "Not very probable". Note their respective backgrounds as architect and stockbroker respectively: for a stockbroker, nothing is certain and he would go for scenarios with the likeliest chance of happening while for an architect, anything is possible and he has to weigh all possible avenues before continuing.
On the subject of #8's profession, two of his most important points were likely only considered because of his background in civil architecture. Who *but* a city architect would know exactly how long it takes an El Train to pass a given point? And it's certainly no coincidence that his dispute with the the testimony of one of the witnesses stems from an observation on the length of the man's hallway.
Modern audiences are often confused about why most of the characters are protective of elder men in general and #9 in particular. Given the time the film takes place, #9 would have been born in the final decades of the 1800s, which means he would have lived through the First World War (and probably fought in it), the Spanish flu, the Great Depression, and then the Second World War with all its deprivations: for having made it through all that, he deserves a certain respect.
Juror #11 takes his jury duty so seriously because he comes from an Eastern European country that probably would have been a communist dictatorship at the time the trial took place; as such he appreciates everybody getting a trial with due process, rather than a show trial or simply being thrown in prison or a labor camp as they would have been "back home".
A lot of the Juror's personalities are based on their jobs.
Juror #1 is a football coach; he's trying to 'coach' his fellow jurors.
Juror #2 is a bank clerk; bank clerks work in quiet environments, which explains his meek nature as he's not so used to an environment as hostile as the juror room.
Juror #3 operates a messenger service; constant package deliveries would stress a man out.
Juror #4 is a stock broker; the kind of job that would require you to be factual and keep a cool head in high-pressure situations.
Juror #5 is a health-care worker; these kinds of people have constant sensitivity when dealing with people who are sick or injured.
Juror #6 is a house painter; while a generic job that also coincides with his role as The Generic Guy, painting requires principle, which he has.
Juror #7 is a salesman; him being impatient does make sense since when he does his sales, he doesn't stay anywhere for a long period of time.
Juror #8 is an architect; he looks at all angles from the case like he would when developing architectures.
Juror #9 mostly likely might be a church pastor based on the "sermon" comment made by one of the Jurors, which explains his wise nature.
Juror #10 is a garage owner; pushiness is sort of a common trait in garages.
Juror #11 is a watchmaker; him trying to piece all facts together is like trying to put all the cogs in a watch together.
Juror #12 is an ad executive; having to constantly choose between ads isn't all that different from constantly choosing between guilty and not guilty.
A storm is slowly building all throughout the first half, with the jurors' room getting increasingly hot and dark as Juror #8 struggles to convince the others to join him in a "not guilty" vote. The storm finally breaks, the lights are turned on and the fan starts working only once the vote reaches an even split of 6-6 and the hardest part of #8's job is done.
In the 1957 film, all of the jury are white men, which initially leads them to think they have a lot in common and are in agreement with the trial verdict. But it quickly becomes apparent they are quite different and that leads to them approaching the trial differently.
Phil Rosenzweig: Many of the twelve would have looked around the room, and, seeing other white men, assumed that they had much in common and should be able to reach a verdict without difficulty. As they deliberate, however, fault lines begin to appear—by age, by education, by national origin, by socioeconomic level, by values, and by temperament.
Whether the boy is guilty or not, by the end of the movie a murderer is still at large. Especially if the boy is innocent, meaning someone who murdered an old man for seemingly no reason is still at large.
