According to Galen Strawson,
This is the assumption that we have a pretty good understanding of the nature of matter—of matter and space—of the physical in general. It is only relative to this assumption that the existence of consciousness in a material world seems mystifying. For what exactly is puzzling about consciousness, once we put the assumption aside? Suppose you have and experience of redness, or pain, and consider it to be just as such. There doesn’t seem to be any room for anything that could be called failure to understand what it is.