In other words, the “trick” was revealed in advance.
Would you like to guess the percentage of the participants in the second group who solved the puzzle correctly?
Even though they weren’t instructed to restrain themselves from considering such a solution, they were unable to “see” the white space beyond the square’s boundaries.
The correct solution, however, requires you to draw lines that extend beyond the area defined by the dots.
At the first stages, all the participants in Guilford’s original study censored their own thinking by limiting the possible solutions to those within the imaginary square (even those who eventually solved the puzzle).
In the 1970s, however, very few were even aware of its existence, even though it had been around for almost a century.
If you have tried solving this puzzle, you can confirm that your first attempts usually involve sketching lines inside the imaginary square.
There seemed to be no end to the insights that could be offered under the banner of thinking outside the box.