The more correct way to say "fully grok" would be "grok in fullness," anyhow. It is possible to grok but not in fullness; Valentine Michael Smith said this once

The more correct way to say "fully grok" would be "grok in fullness," anyhow. It is possible to grok but not in fullness; Valentine Michael Smith said this once in the book ("I grok but not in fullness"). I'd say it's been live jargon ever since Stranger came out, jumping from SF to the tech world as things often do, and I'm pleased to see it survive despite the modern distaste for Heinlein in many (but not all) SF circles.