An idea blatantly stolen from Pragmatic Thinking. The following passage is taken from the book:
This notion of combining two different, incompatible ideas is the very definition of creativity according to researcher/philosopher Arthur Koestler. In his model, some particular topic area forms a particular frame of reference. The sudden switch from one self-consistent frame of reference to a different, unexpected, incompatible frame of reference is the basis of a strong metaphor. That junction of the two different frames is called a bisociation.
The more unlikely the association—the further apart the frames of reference—the greater the creative achievement when bisociated. This idea is the basis of Edward de Bono’s Po technique. Po is an invented word that tries to go beyond the binary notion of “yes” and “no.” Several techniques involve Po; for now, you might think of it as a super-powerful version of suppose.
One of the Po techniques is random juxtaposition. You take a word from your subject area and combine it with a completely random, unrelated word. For instance, consider the words cigarette and traffic light. The challenge is to form a bisociation from these completely unrelated ideas. For example, cigarette and traffic light might meld into the concept of using a red band on the cigarette as a stop-smoking aid.
The further away the ideas are, the harder it is to join them in a metaphor that works.