In 1927 Russian psychologist Bluma Zeigarnik identified a phenomenon that came to be known as the Zeigarnik effect, which states that waiters are good at remembering particulars of a restaurant bill—until the bill is paid. “Unfinished tasks are remembered approx­imately twice as well as completed ones,” concluded Zeigarnik.

During the eighteenth and nineteenth centuries, most of the Katanga region in what is today the Democratic Republic of Congo was dominated by Luba kings. A powerful secret society known as the mbudye (men of memory) created handheld wooden objects called lukasa (long hand, or claw) as mnemonic aids to maintain oral narratives about fundamental aspects of Luba culture.

“There is one thing at which I cannot sufficiently wonder,” wrote Pliny the Elder, “that of some trees, the very memory has perished, and even the names recorded by authors have passed out of knowledge.”

Advocating in 1790 for the adoption of card catalogues, the German librarian Albrecht Christoph Kayser cited the “common mistake of employees that they believe they will live forever.” Workers “arrange their shops without regard for their successors, considering them well kept in their own memory, without written notes, thus making it impossible for those eventually taking their place, or at least making it infinitely more complicated for anyone to pick up the thread of those who have been called to meet their maker.”