In his research on chimpanzees, Köhler observed how they solve problems, such as that of retrieving bananas when they are out of reach. He found that they used wooden crates as makeshift ladders, in order to get the food. When bananas are located far away chimps used sticks to get them. Köhler concluded that the chimps had not arrived at these methods through trial-and-error, but because they had an insight. They carried it out in a way that was, in Köhler's words, "unwaveringly purposeful."