Full Idea
Only a theory that explained conscious events in terms of unconscious events could explain consciousness at all.
Gist of Idea
Conscious events can only be explained in terms of unconscious events
Source
Daniel C. Dennett (Consciousness Explained [1991], 14.4)
Book Reference
Dennett,Daniel C.: 'Consciousness Explained' [Penguin 1993], p.454
A Reaction
This sounds undeniable, so it seems to force a choice between reductive physicalism and mysterianism. Personally I think there must be an explanation in terms of non-conscious events, even if humans are too thick to understand it.