The average person can rarely hold a thought for more than three or four seconds, eight at the most, before the mind wanders. It's very unusual to be fully conscious for more than a tiny window of time. That is, unless you're having a conversation with someone else, in which case you can often do it for long periods of time, especially if the conversation is with someone you find particularly interesting. In other words, most of the time we're conscious is when we're talking to someone else, or otherwise interacting intensely; during moments in which when we're not clear whose mind is whose.
Where is this from, I almost don't believe that.