I disagree with this completely. The level of difficulty is just enough to get the brain properly churning with a manageable level of frustration without being completely impossible.
I never said this isn’t a fun tricky-but-not-too-tricky one-off puzzle for out-of-practice adult puzzle solvers. (It has one key trick that someone who doesn’t do very many puzzles might take a while to figure out.) I only said it was pretty easy for me personally.
I further claimed that if you want to train complete novices (I am thinking of my 6 year old here, or his less experienced 6-year-old friends) to solve very hard variants of this puzzle, you should start with easy puzzles and introduce one new trick at a time. If your goal is not to train novices to solve hard puzzles, then feel free to disregard this advice.
There are some fun harder tricks that you can throw into this genre of puzzle (not included in this particular example) that if you tried presenting to my 6 year old would completely stump him. But after working his way up methodically he could be taught to notice and solve them.
