The Buddha taught that the six sense spheres of hearing, seeing, sensing, smelling, tasting and cognizing represent "the all". The Bahiya Sutta points directly to the sense spheres as not-self.
Dukkha is an inevitable part of life, the 1st Noble Truth. How we meet it and work with it is a key issue of practice. If understood, it can be a doorway to liberation.
All experience arises and passed in the vast space of awareness. This meditation, adapted from Tibetan text, directs attention to awareness itself rather than the objects within the awareness.