Given any account of the physical processes purported to underlie consciousness, there will always be a further question: Why are these processes accompanied by conscious experience? For most other phenomena, such a question is easily answered: the physical facts about those processes entail the existence of the phenomena. For a phenomenon such as life, for example, the physical facts imply that certain functions will be performed, and the performance of those functions is all we need to explain in order to explain life. But no such answer will suffice for consciousness.
