I really love this quote from Dosho Port:
"When we come to practice we don't know what we don't know. After a while, the ego mask starts to crack and we begin to know what we don't know. With some diligent practice, we might have a break through and for a moment or so know what we know. And if we continue with this wondrous work, we might stumble back to not knowing what we don't know."
If this seems discouraging, Dosho says this process can be like a spiral, in which one never returns to the same place.
"Not knowing what we don't know" means that we accept conventional views as all there is to "reality." I would argue that the path of the Buddha begins with the acknowledgment that our conventional views are not all there is to reality. We perceive there's something we don't understand, and we accept that this something cannot be understood by intellect alone.
The Web is well infested with people who fancy themselves to be experts on Buddhism because of their superior intellectual understanding. But most of the time, these "experts" are people who don't know what they don't know. And because their cups are full of certainty, they are unlikely to continue on any kind of path.
IMO the biggest advantage of working with a teacher is that a good teacher will pull rugs out from under you whenever you feel satisfied with concepts and theories.
On the other hand, Dosho says, "Some of us tend to cling to this beginning movement as if the idea 'I don't know' is all there is to practice. That's a sad thing." Perhaps the assumption that there is nothing to be realized or clarified is another kind of certainty.