You learn 20 new words, feel confident – and three days later half of them are gone. That is not a sign of a bad memory, it is completely normal. Back in 1885, the psychologist Hermann Ebbinghaus described how quickly freshly learned material decays: the forgetting curve.
Without repetition you lose most new information within the first 24 hours – after that the loss levels off. The key insight: every repetition at the right moment lifts the curve back up and makes it flatter. The knowledge decays more slowly next time, and the intervals can grow. After four or five well-timed repetitions, a word often sticks for months.
This is where most people go wrong: they either never repeat, or cram everything at once (the night before the exam). Both work against the curve. Far more effective is spaced repetition – a system that shows each word again exactly when you are about to forget it. The 1000 Words vocabulary trainer handles this timing automatically: each day you only see the words that are due.
A second lever against forgetting is sleep. During deep sleep the brain moves what you learned into long-term memory – so hearing exactly the day's words again in the evening feeds that process. Combining active training during the day with calm listening repetition at night works with the forgetting curve instead of against it. What would otherwise have to be relearned again and again finally stays.