If you take a person who has always been in a rural area into a big city, he will be probably be kept awake at night by the sounds of police sirens, garbage trucks, doors slamming, etc. If you bring a city person into the country, he will be kept awake by dogs barking, crickets chirping, tree branches rustling, etc. They are both used to noise, but when the noise is different from what they are used to, it is disturbing. This is because we learn over time that some sounds are normal and harmless in the place where we live and can be ignored. We do the same with sight, though we are less aware that this happens. Two people walking down the same street don't see the same things. We filter out what we have learned is not important.
    Unfortunately for those of us who want to develop our spiritual side, a lot of the sights, sounds, and scents that we don't notice because we have learned to filter them out, are the spiritual ones that can help us develop spiritually. When we were little kids and hadn't developed these filters yet, we saw and heard things that adults told us were imaginary. Eventually, we learned to filter them out of our lives because of what those well-meaning adults told us. 
    So one of the first things we all must do to grow spiritually is to get rid of those filters. To accept once again that there is an invisible world all around us that we ignore, but shouldn't.