I’d be happy to discuss epistemology, but whether the juror is right or not is not the issue. You seem to think that I wouldn’t make the same point if I realized how wrong jurors could be. This is not the case. Juries are made of human beings who have flaws and make mistakes and that is part of the system. Convictions and acquittals occur because jurors are mistaken and that is absolutely part of the system as it exists now.
Jurors are asked to determine who they believe all the time. Take the murder of George Floyd as a recent very highly publicized trial. In that trial the prosecution called a witness saying that Floyd died because the knee of his neck asphyxiated him. The defense called a witness saying that Floyd died because of drug use and a pre-existing heart condition. Both of these witnesses had credentials as people who were capable of making such determinations and those credentials were offered to the jury.
So the jury went into deliberations with there two conflicting stories. If they believed one witness then they convict, if they believe the other then they acquit (or at least it’s easily believable that a conviction could hinge on this). The prosecution, in their closing statement, told the jury they were allowed to believe their eyes, that they saw what they saw. Lawyers commenting on the case said that this was hard for the defense because jurors had knees and jurors had necks, and odds are they are going to understand that you can asphyxiate someone by applying one to the other.
So I am quite sure, from recent precedent that a juror is 100% allowed to apply their knowledge (or their belief) about whether or not a person could asphyxiate in a given position to their deliberations in a murder trial. The prosecution told them so and the judge didn’t warn anyone, the defense didn’t object, there was no mistrial.
They can also apply their “knowledge” (that is, their prejudices) of human psychology in determining which expert witness was more “credible”. They can also apply their prejudices about different schools or other expert qualifications to determining which witness was more credible. And they can say to themselves, “The [prosecution or defense] just paid that guy to say that, I think it was complete bullshit!” and utterly disbelieve it. And I know that’s true because witnesses for the prosecution in that case volunteered to testify without being paid to make their testimony more credible.
Twelve people, with all of their flaws, make a determination. That’s the system.
Like, when you say that if a juror knew where a tree was they would have to alert the court to this forbidden outside knowledge, is that based on your knowledge of actual court procedure, or are you just saying how it seems to you? I can’t even imagine how such a system would work and how jurors would categorize knowledge and beliefs they were allowed to use vs. knowledge and beliefs they were not allowed to use (speaking of epistemological issues!).