To put it briefly, the easy questions are about the content of consciousness, the hard question is about the existence of consciousness itself. The hard question is hard because it doesn't seem to arise just from lack of knowledge. It isn't simply a matter of increasing our understanding of how the brain works. The difficulty is rather that we don't seem able to say what sort of explanation is needed to solve the problem. Not everyone, it has to be said, admits the existence of a hard problem.
Some writers simply deny that there is anything to be solved at all.
They say that brain function and inner experience are really the same thing, and that it is an error on our part to think they are different. They are, however, in a minority, although only a few today are willing to go to the opposite extreme and to speculate that consciousness may be altogether non-physical. Cairns-Smith is not one of these, but neither does he deny the existence of the puzzle. First, consciousness is a physical effect, although not necessarily one that is understandable in terms of present-day science. Some modulations of consciousness are self-generated.