Problem-solving is one of the most obvious functions of thinking. Several processes have been proposed to account for effective problem-solving.
During World War I, Gestalt psychologist wolfgang Koehler studied the practical problem-solving of chimpanzees. For example, a chimpanzee inside a cage reached without success for a banana out of reach just beyond the bars. There were two short hollow sticks, one thin and one thick, inside the cage, but neither was long enough to rake in the banana. Suddenly the chimpanzee seized the two sticks, assembled them by pushing the thin one partly into the thick one, and successfully used this� new long tool to retrieve the banana.
Koehler characterized the chimpanzee's problem-solving discovery as an example of insight, the perception of a problem in a new way. Insight is often described as sudden or surprising, giving rise to the exclamation "Aha!" or "Eureka1" (I've found it).