Retrieval should be effortful — but does that mean harder is always better?

No. Retrieval must be effortful but mostly SUCCESSFUL; blind guessing with no feedback helps very little.

The sweet spot is desirable difficulty: hard enough that you have to work to reconstruct the answer, but not so hard that you simply fail and guess randomly.

• Effortful successful retrieval → strong strengthening.
• Blind guessing with no feedback → little benefit; you never actually retrieve the right memory.

If a topic is so new you can't retrieve anything, do some encoding first (read it once), then switch to retrieval. And if you must guess, feedback afterward rescues the attempt by supplying the correct answer to learn.