Grokking being beyond understanding something is central to Valentine Michael Smiths understanding of the world, and therefore the plot, in “Stranger in a Strange Land”.

Grok is not simply understanding or knowing a thing, it’s knowing that thing so well and all the things related to that thing, and understanding all of your feelings associated with that thing, that it becomes a part of you. At least, that was my interpretation of it.

Heinlein’s explanation and exposition is more detailed in the actual book. If you have not read it, highly recommended.