Why are puzzles puzzling?

Why are puzzles puzzling?

Here is my basic answer. It will become more refined as the semester goes on.

From a psychological standpoint, our set of normal associations about the elements of the puzzle omit the key association(s) needed to solve the puzzle. But the key associations are there, for those who have the eyes to see. (See the "Two Rings Problem" below for an example.)

From a theoretical standpoint, there is potentially an infinite number of relations among the puzzle's elements, so it can be difficult at times to narrow down to the key ones. (See the post "Two Books on a Bookshelf" for an example.)

Psychological Example: "Two Rings Problem" (created by Andrew Cohen)
Suppose you had to fasten together two steel rings (each eight inches in diameter and each weighing eight pounds) by using only a long candle, a strike-anywhere match, and a cube of steel (two inches on each side). The rings need to be securely fastened so that when one ring is picked up the other ring will follow.

When you want to know the answer, go to the next post "Solution to Two Rings Problem."