I had jury duty for one month when I lived in DC. A big room of us gathered in the morning, waiting around for a panel to be called or for the manager to call it a day. It was boring, but the juries were interesting. I think I was called for 4 cases, got on three juries. The fourth was a marijuana case. I took the position that I couldn't be objective and was excused by the judge. I look back on that now with some amazement--I think in the same situation today (though I'm too old for Fairfax juries) I probably wouldn't say a thing. Did my opinion of pot change? Perhaps. But I don't remember ever believing in legalizing it; decriminalize it was, I think, my likely position in the early 1970's. These days I don't know; I've probably voted to legalize it but I don't know if it's the right answer. It's the popular position these days, but I'm not totally convinced it's working out.
Bottomline, I'm less confident now, because I'm older, have seen more, have changed my opinions more.
How does this tie to historians? A juror is required to put aside one's personal feelings and convictions and become an objective trier of fact. That's what I couldn't commit to back then. I'd argue a historian as a teacher is required to do the same; as a research scholar also.
