Appropriate past experience, while necessary, does not guarantee a solution. Insight will come easily only if the essentials for solution are arranged to that their relationships can be perceived.
For example, a chimpanzee solves the stick problem more readily if the stick is on the same side of the cage as the food. He has more difficulty if he must turn away from the food to see the stick. Human brings can do much of their rearranging of a problem mentally; they can form a mental image of the situation and rearrange objects in that image in an attempt to find a solution. Mental manipulations may it times go on preconscious, and only when a solution has been found does the person suddenly realize that he had been thinking about the problem.