Most people like to think of themselves as flexible and willing to change their minds in response to new evidence. However, we of course notice that others are very stubborn, and there's some psychological literature suggesting that people in general don't change their minds as much as they'd like to claim to. On the other hand, there are interesting studies in the other direction, suggesting that people mis-remember their past views as being more similar to their present views than they really are, so that surveys on whether people changed their minds will get misleading results if they rely on comparing remembered views to current views. So perhaps people are right to think that they change their minds, despite the fact that tricks of their memories leave them without much evidence to back it up.
Anyway, since I tend to have a hard time thinking of examples of changing my mind on demand, I thought I'd write about a significant change in order to increase the chances that I'll continue to remember it when I need an example. I was originally in favor of the invasion and occupation of Afghanistan. I expected we'd make a mess of it, especially with Bush directing things, but the Taliban were so awful that I thought the mess we'd make would still be a considerable improvement.
I now think we should probably withdraw from Afghanistan. I do still have some tendency to think that there could be better ways of doing things which would make our intervention helpful, but I can't see any politically realistic path from our current policies to anything which would be significantly more productive. In particular, I think we'd probably have to give up the goal of suppressing opium cultivation in Afghanistan, and I don't see any chance of that. I was aware of this issue in the past, but I apparently underestimated other issues and the results of the various problems interacting; I did not imagine that an Afghanistan with a large U.S. military presence would ever end up with the Taliban again controlling most of the country. Further, the Karzai government is not nearly as much better than the Taliban as I would have hoped; it appears to be quite horribly corrupt, which isn't really a surprise, but it even has some pretty horribly retrogressive policies on women (the big issue where I thought the Taliban were bad enough to make their removal a goal which overrides almost everything else).