The Spacing Effect

German psychologist Hermann Ebbinghaus published *Über das Gedächtnis* (*Memory: A Contribution to Experimental Psychology*) in 1885. He experimented on his own memory — memorizing large numbers of nonsense syllables (such as "DAX" and "ZOF") — then tested himself at different time intervals to see how much he retained.

He discovered two things. First, the Forgetting Curve: memory drops sharply after learning, with 70% lost within 24 hours. Second, the Spacing Effect: the same amount of study time, distributed across different days, is far more effective than concentrating it in one session — and the longer the interval between repetitions (as long as it's not too long), the more durable the long-term memory.

But the Spacing Effect has a condition that's often overlooked: each repetition must provide a new angle or new information. Ebbinghaus found that mere repetition (seeing exactly the same content) was far less effective than "re-encountering the same concept from a different angle." Later psychologists called this "Elaborative Rehearsal" — adding new associations with each reappearance deepens the memory.

If your follow-up emails always say "our product is great," that's noise — the meaningless syllable repetition from Ebbinghaus's experiments, which the brain filters out as noise. If each one brings "something about you that you didn't know," that's intelligence. The spaced repetition of intelligence gets remembered. The spaced repetition of noise gets deleted.