I just recently served on a jury.
I’ve been a registered voter since I was 18 and I’m on most of the lists that they say they gather names from (tax records, driver’s license, voter registration, etc) but it took them over 30 years to finally call me in for jury duty. I can’t say I was looking forward to it, but overall it wasn’t so bad.
In my county, you get called up and you have to show up each day for about a week. You sit in a big room with a bunch of other potential jurors. Periodically, the computer selects a “panel” of jurors (I believe 32, typically). That panel is taken up to the courtroom and questioned, and then the prosecution and defense take turns crossing people off of the list until they get down to 12. If you are selected, then you sit on the jury and, if the trial finishes before the week is done, you go back into the big room and back into the pool of potential jurors. It was all random, so you could potentially serve on a different jury each day you are there, or you might not get called up at all, or anywhere in between. Some people served on two juries that week. Others didn’t serve on any.
In my case, Monday was a holiday so I didn’t have to report until Tuesday. I sat and did nothing all day Tuesday and Wednesday. On Thursday I was finally called up for a panel. After the questioning, I was selected for the jury.
It was a short trial. The jury selection was done in the morning and the prosecution and defense both made opening statements. Then we broke for lunch. The prosecution called two witnesses. The defense did not call any. The defense also did not present any evidence. The prosecution and defense made their closing statements, and we deliberated for 15 minutes. We found the defendant guilty on one charge and not guilty on the other. The first charge was pretty straightforward. The second one was more circumstantial and there just wasn’t enough evidence to prove that the defendant was guilty on that one. A few minutes into the deliberations we took a quick vote just to see where we were, and we were all unanimous on the not guilty for the second charge, and 11-1 on guilty for the first. At that point there was no sense even discussing the second charge any more so we focused on the first.
The trial was over by about 3:00 pm and the judge told us that we didn’t have to come back on Friday.
It wasn’t that bad of an experience. The two days of sitting around doing nothing were a bit boring.
Yeah, but you just about can’t swing a cat in Silicon Valley without hitting an engineer. 
FWIW, I’m an engineer and I was selected. I’m in southern PA, an area where the engineer density isn’t quite so high.
I have friends and relatives who are police officers. That didn’t stop me from being selected either.
In the jury I served on, we were given a list of charges and the conditions required for the defendant to be guilty on each charge. The judge’s instructions were that the prosecution would present evidence (not facts) and the defense may or may not present evidence, and that a lack of any defense is not evidence of guilt. The judge made it very clear that it was the jury’s job, and no one else’s, to determine the facts in the case. We were to base our decision on the evidence presented, and “common sense”.
Based on that, if one juror understands that the facts presented don’t make sense, they can say why and if the other jurors agree, then the jury can certainly find that the facts of the case are not as the prosecution presented them.
That is my understanding of it, as a recently served juror, based on the instructions that the judge gave to us.