Memory retention falls rapidly at first and then more slowly, in the absence of rehearsal.
Ebbinghaus tested himself on nonsense syllables in 1885, losing over half within an hour and stabilising thereafter. Several functions approximate forgetting and his savings data are not a universal exponential law. The curve's practical use is inverted: spaced review flattens it.
In practice
- A trainee retains almost nothing from a Friday briefing by Monday, and nearly all of it if reminded on Saturday and again on Tuesday.
- A language learner who studies for six hours on Sunday remembers less than one who studies forty minutes daily.