It would perhaps be tempting to say that the difference between a necker cube and something genuinely tension-inducing is that things like necker cubes just hijack a preexisting quirk of our perceptual system, they don’t create entirely new perceptual/cognitive tangles.
But that might be a coincidence, not a real distinction. It seems like anything can become a source of tension in the right circumstances, and the right circumstances being just when something becomes a part of our web of ambiguous images.
A cube on-screen is just a puzzle, but when the solution to that puzzle seems like it will steer us into one picture or another, it becomes something else. It becomes something we need to solve, not just an annoying pull on our innate drive to solve things.
And it’s not like we need sophisticated perceptual illusions to supply us with puzzles. We seek them out. Sometimes we even create them, out of whole cloth. The world is full of situations, and situations, in themselves, are not problems, because there are no levers. There is nothing to solve. But we easily locate or even invent levers or pseudo-levers, turning bare situations into things it seems like we can potentially ‘solve’.
What do those clouds remind me of? Why do the neighbors come and go at such odd times? What’s going on with the spackle patterns on the ceiling…?
Situations become puzzles, because of the way we’re made, to extract patterns. And puzzle become problems, because as soon as those puzzles become a part of our web of ambiguous images, they acquire urgency.
Puzzles are situations that we’ve subjected to pattern extraction, and problems are puzzles we’ve invested with urgency.