A common weak area for CFI initials so be sure to have it down.
Yes I have to understand it thoroughly, especially for the oral, the issue I have with it is that even though it is an outline on how people learn and teaching methods there is ironically not a roadmap or logical way to study the subject, or at least i have not found one, in other areas of study for the CFII there is logical introductions and a flow to learning the subject with FOI I find myself all over the place.
Nothing else for it than re-reading it for the umpteenth time and see if a light bulb goes on.