Why is it so difficult to give up old perceptions when it is clear that what we really know is only a fraction of what there is to be known? The tiny fraction we see is not the only way it is. Whenever we say, "I know it," it means that we no longer want to struggle with other ways of seeing it. But the way we once saw it may not be the way it is now. Certainly the way something is now does not determine that it will always be that way because we are, all of us, on a journey whose ultimate destination is unknown.
People often ask how they can avoid daydreaming when they are trying to meditate. Meditation does not make them daydream, but only makes them more aware of fantasies they have always had. In meditating even for a short time, they hold a mirror up to themselves that clearly reveals the shape of their fantasies.
Walking deep in a forest in late autumn, you may be startled by the loud rustling of your feet among the dry leaves breaking in the stillness. Fantasies disturb meditation in the same way.