I served in exactly one jury, and it was a fairly serious case--vehicular homicide. The defense attorney was among the most famous in Colorado. We were one of the first juries serving under a new law that allowed jurors to take notes, and 10 of us took careful and copious notes throughout the trial. When we started deliberating, the 2 who had not taken notes had a different memory of the trial from the rest of us, and the rest of us were constantly correcting their memories. That was because of the skill of the defense attorney, who lied and misrepresented evidence throughout the trial. For example, during voir dire, he talked repeatedly about the fact that they were going to present certain evidence that would clear his client, and he wanted to know if we would accept that evidence when it was presented. Every juror heard that every time a potential juror was interviewed. During his summation, he emphasized how important that evidence was, and he reminded us that we had heard it said many times. That alone was enough to convince the 2 who had not taken notes. The 10 who had taken notes had to point out that the defense had never actually presented that evidence--we had indeed heard it many times, but only from the attorney himself during voir dire and his summation. The prosecution had presented clear testimony that it was not true, and that testimony was not challenged by the defense; the defense never brought it up themselves.
The amount of evidence presented to a jury can be overwhelming--far too much to remember. A skilled attorney can manipulate a jury by playing to their inability to remember it all. Couple that with the fact that people who are experts on the topic of the trial are not allowed to serve, and you have a perfect recipe for incorrect verdicts.