The old-school way, with the chief scout having it all in his head, gave no continuity. If he gets run over by a bus he takes all the knowledge with him.

"I have actually gotten to revisit, in my head, all the museums I've ever gone to."

"Kids disappear into imaginary relationships all the time" . . . but "usually there's a limit to how far that imaginary relationship can go, because it's all in their head."

When a neurologist ruled out medical causes like Lyme disease, Ms. Abaspour recalled, her husband said, “I think we should just give her a placebo — it’s all in her head.”

The tape was the piece of evidence that assured Cohle that this grand conspiracy wasn't all in his head.

Captain Whalley, who seemed lost in a mental effort as of doing a sum in his head, gave a slight start.

In one's head

Meaning

Prep_phrase