The first group was given the same instructions as the participants in Guilford’s experiment.
The second group was told that the solution required the lines to be drawn outside the imaginary box bordering the dot array.
In other words, the “trick” was revealed in advance.
Because they hadn’t, they were obviously not as creative or smart as they had previously thought, and needed to call in creative experts. The nine-dot puzzle and the phrase “thinking outside the box” became metaphors for creativity and spread like wildfire in marketing, management, psychology, the creative arts, engineering, and personal improvement circles.
There seemed to be no end to the insights that could be offered under the banner of thinking outside the box.