How do we use it?

Put your thinking in the opposite direction. Write a question that can be asked about the topic you are thinking about, then link it with the completely opposite question. 

After that, develop some answers to this reverse question.

Why its important?

You might feel a bit strange developing "reverse questions," but you will find that as you work on answers to your "reverse question," you are able to generate great (opposite) ideas for your original question.

Example:

Instead of "How can we encourage people to eat healthy foods?", we'll reverse it to "How can we encourage people to eat fast foods?" 

Some answers: 

Allow fast food companies to advertise when children are watching television.

Place huge, charming posters of fast food all over schools.