off the top of one's head

The value of Greek prose composition, he said, was not that it gave one any particular facility in the language that could not be gained as easily by other methods but that if done properly, off the top of one’s head, it taught one to think in Greek.

“Our next firework demonstration will illustrate how catastrophic it can be to ignite a shell within a mortar off the top of one’s head,” a spokeswoman droned into a microphone on a recent June morning, while a small crowd gawked at a mannequin bro in a red shirt, posed with its hands clamped around a reloadable tube aerial shell firework balanced against its plastic skull.

But classifying a life packed with as many rich, diverse experiences as Paterno's can be more complicated than screaming off the top of one's head.