The most difficult puzzle I can conceive would by happenstance use pieces of exactly the same shape and size. To be particular, the puzzle would be a large
hexagonalshape with at a minimum a thousand pieces, each of which would be hexagonal as well. Because the outer lines of the larger encompassing hexagon would be made of those smaller hexagonal components, the puzzle simply would not have any 'straight' edges at all. It's edge would simply be the jagged
pattern of an outer row of hexagons.
The subject of the puzzle would be the
color gray. Essentially, then, it would be a light gray tone, fading slightly off-center toward a barely lighter shade of that same gray amorphously floating inside it, with a subtle but constant fade from edge toward center. By my reckoning, it would be possible to make such a puzzle with precisely
one correct solution, and possible again (though perhaps requiring some advanced technological aid) to determine whether the puzzle was indeed put together correctly or incorrectly. But it would likely drive a man mad to try to get all those very similarly shaded hexagons not only in the right place but each in the correct
orientation.
Confessedly, on the other hand, if the sole judge of the correct completeness of the puzzle is the human eye, and not a mechanized certifier, the pieces fitting so easily together might prompt the puzzle solver to simply put together the hard-to-distinguish pieces in a 'good enough' approximation of the intended final outcome, at which point they will humanly declare victory and pat themselves on the back. Perhaps, then, an even more devious effort would be to make a puzzle composed of nothing more than extremely narrow concentric circles of a dozen or more bands of iridescent and shifting
rainbow colors laid out in no particular order. Now that I've thought about it, I am going to create just such a puzzle and gift it to somebody
I wish to give the gift of
madness.