Another title: Physics of opinions.
I think it's like magnetism, which exhibits hysteresis. [...]
A lot of things behave like this, and opinions are one of them. We all have pre-formed opinions - imagine the bottom of the graph is "free trade is good". If we accumulate evidence that leads us to change our mind we move to the top "free trade is not so good" line. Now suppose we hear some more evidence that pushes us the other way - do we switch back right away? No, we hang on to our existing beliefs until the weight of evidence becomes unavoidable. Switching basic views is a big thing, and we can't be forever changing back and forth.