When a trivia question makes you itch for the answer, why does the answer stick better?

Answer: Wanting the answer makes the brain treat it as a reward worth remembering.

Feeling that the answer matters makes attention hold the fact more firmly in mind. — Importance and attention can improve memory, so this explanation is tempting. But the curiosity effect appears even for low-stakes trivia that has little practical importance. The critical state is wanting the missing answer, not deciding that the fact is valuable enough to store.

Being surprised by the answer makes memory store it more vividly afterward. — Surprise can boost memory, so this is a neighboring idea. But curiosity studies measure the wanting state before the answer appears, not only the reaction after it. An answer can stick because the question made you hungry for it even when the answer itself is not shocking.

Wanting the answer makes the brain treat it as a reward worth remembering. ✓ — Right. Curiosity is a wanting state: the question opens a gap, and the answer arrives while that gap is still active. Research links this state to reward-related brain activity and to memory systems such as the hippocampus, so the answer is learned under stronger motivational conditions. The key is anticipation of the answer, not a judgment that the fact is important or a shock after it appears.