He gave a group of students a box of pins, a candle and a matchbook – and told them to find a way to attach the candle to the wall. They were stumped. Some of them attempted to melt the candle to the wall; others experimented with pushing the drawing pins through the wax into the wall, with little success. In fact, there was a simple way to solve the problem: tack the box to the wall and put the candle inside it.
But very few of the participants thought to do so. Why? Duncker thought the answer lay in what he called ‘functional fixedness’. When we see an object, we become fixated on its main function – in this case, the box was holding pins, and so nobody thought that it could hold a candle. This limits our ability to think critically about what is possible.