What is functional fixedness?

Functional fixedness is when people cannot see past the original use of an object. For example hammers are for putting in nails - nothing else. If you found yourself in a position where it was windy and things were blowing away it would not occur to people that the hammer could be used as a weight - because this is not what a hammer is for.

This is why conducting proper user interviews can unearth interesting insights that standard questionnaires cannot. People sometimes cannot imagine something for more than it is.

The classical example of this is the 1945 experiment where participants where given a candle and a box of tacks. They were asked to affix the candle to the wall such that the wax would not drip on the floor. Very few people took the tacks out of the box and affixed the box to the wall to hold the candle and prevent it from dripping. If the tacks were taken out of the box and the user was presented with an empty box, participants were twice as likely to solve the problem.