Only 20 percent managed to break out of the illusory confinement and continue their lines in the white space surrounding the dots.
The symmetry, the beautiful simplicity of the solution, and the fact that 80 percent of the participants were effectively blinded by the boundaries of the square led Guilford and the readers of his books to leap to the sweeping conclusion that creativity requires you to go outside the box.
Today many people are familiar with this puzzle and its solution.
In the 1970s, however, very few were even aware of its existence, even though it had been around for almost a century.
Guilford was one of the first academic researchers who dared to conduct a study of creativity.