If this image represented a stack of learning modules rather than rocks, the student could not fully understand all of the material without the small piece on the right.
For example, what if a sequence of learning in mathematics was to be taught from the bottom up: start with the rock on the bottom – geometry. Add the next component, trigonometry. Begin to gain an understanding of the next set of information – differential geometry…but in order to move on to topology, fractal geometry and further – at some point the structure would not hold together without an essential but small outlying piece, like philosophy, to keep all the modules balanced.
If students could be shown a whole picture of completed and balanced learning sequence, they may feel more comfortable with difficult material along the way because they would be able see the points in the process where they are supposed to feel unbalanced.