Here's an interesting story from the Boston Globe archives. Opening pars:
"When people think of knowledge, they generally think of two sorts of facts: facts that don’t change, like the height of Mount Everest or the capital of the United States, and facts that fluctuate constantly, like the temperature or the stock market close.
But in between there is a third kind: facts that change slowly. These are facts which we tend to view as fixed, but which shift over the course of a lifetime. "
The story goes on to explain that what you think is true might have once been true, but might not be true any more... and it warns of the dangers of not keeping up with those slow changes that creep up on you and alter your reality.