“Those who do not know the torment of the unknown cannot have the joy of discovery.”
The important thing to realize is that the conjuring up of the idea is not a deliberate, voluntary act. It is something that happens to us rather than something we do.
In ordinary thinking ideas continually ‘occur’ to us in this fashion to bridge over the steps in reasoning and we are so accustomed to the process that we are hardly aware of it. Usually the new ideas and combinations result from the immediately preceding thought calling up associations that have been developed in the mind by past experience and education.