What you have learned about yourself in the role of being an observer of Vietnam and 20th century events?
Of course, there are many things that we could learn from these things. For me, the main lesson of Vietnam is that I do not know how good I am at understanding the true importance of events as they happen. It is much easier to determine how important something was in hindsight. I hope that this makes be a little more humble about my opinions in the present. I worry that it means that I lack wisdom.
When I study the Vietnam War, it is easy for me to see how people would have made mistakes and gotten us into that war. It is easy to see how they might have thought the war was necessary and winnable. This means that it would have been very hard to have lived at that time and to have had the right opinion about the war (or what looks right to us today).
When I think about this, it makes me realize that I do not really know if we are analyzing threats properly today. I do not know if we are taking certain threats too seriously or not. This is humbling and a little bit scary because it makes me realize how easy it is for us to make really costly mistakes in our policies.