What are the disadvantages of spaced repetition?

What are the disadvantages of spaced repetition? The main ones are review debt, boredom, a bias toward isolated facts, and the work of making good cards. None of them break the method, but they are why people quit it. Spaced repetition is still one of the best-evidenced ways to remember vocabulary. The downsides are about the daily reality of keeping it up, not about whether it works.

• Review debt piles up. Miss a few days and the due cards stack into a wall you do not want to face, which is the most common reason people stop.
• It gets boring. Flipping the same cards is dull, and dull habits get skipped.
• It favours isolated facts. Spacing is great for single words and their meanings, weaker for stringing them into speech, so it cannot be your only practice.
• Good cards are work. Writing clear cards with real example sentences and audio takes time, and bad cards waste every review after them.
• It needs consistency. The payoff comes from short daily sessions. Skip them and the schedule falls apart.

Most of these come down to the manual grind. A scheduler that adapts to how well you actually recall each word, and that builds the cards for you, removes the two biggest quit points. Here is how an adaptive schedule cuts the review pile down.