Is it important that the reality of things doesn't exist, instead of just behaving like things don't exist? In some traditions their philosophy says that concrete things don't really exist, only in the mind like just an experience. But is that vision important, or could just your relation to those things as if they don't exist be enough? In other words, is this philosophy just a way to concentrate on the spirit, instead of the outer world, or do they really mean this?
Whatever that exist outside we experience through our sense doors and paint a picture in our minds. This metal model we construct will not exactly correspond to what is outside will not the exactly the same from person to person depending on many factors like cognitive ability, sharpness of senses, etc. Hence that we know about the world is not perfectly in touch with reality and not always exist as we expect it to be. So it would be safe to say that anything we perceive as such does not exist in such a form that we perceive or expect it to be in. Also our outlook of the world is mentally constructed and does not exist in any form we expect or think it to be in. Also we have no ability to exactly know what exactly the world is as we are limited by cognitive ability and or faculties. So we will never know the world as it is, perhaps unless you become a Buddha as only Buddha can see all phenomena.