There are two things necessary in order to perceive: One thing is openness, the other thing is effort made in that direction. When contemplating upon anything the mind must be free from all else that stands in the way; that is called openness. Also one must arrive, by the help of concentration, at focusing one's mind on a certain object. The next thing is to be interested enough in all things that one comes in contact with and one cares to know about, that one may penetrate below the surface and find out what is hidden in all things.