Until proven otherwise, we should assume that consciousness doesn't play a role in human behaviour. This is the conservative position that makes the fewest assumptions.
--- Robert Provine, quoted in Mark Buchanan, Why we are all creatures of habit, New Scientist 7 Jul 07, p. 37
Other quotes along the same vein:
Alex Pentland: "The data support the view that a lot of human behaviour is largely automatic and determined by instincts alone."
Ap Dijksterhuis: "Almost everything we do is automatic. I'm more and more inclined to draw the conclusion that consciousness is a pretty unimportant thing."
Buchanan writes: "Provine goes even further. He suspects we only think we act consciously because our inner voice is so skilled at making up seemingly reasonable narratives and explanations of our unconsciously generated behaviour."
There's a resonance with Michael Brian Schiffer's theory of communication that focuses on receivers and artifacts rather than senders and words. From the article: "Researchers studying apes and other animals typically start from the idea that animals' actions follow mechanically and automatically from their instincts alone. In contrast, psychologists tend to view people as mostly self-aware individuals acting on conscious thoughts. Pentland's idea is that if we can explain and even predict much of what people do without ever referring to their words or conscious thoughts, then maybe those aren't as important as we usually believe. It is a radical thesis, but one for which his sensors provide strong support."