Paul Graham notes:
In 1989 researchers tracked the eye movements of radiologists as they scanned chest images for signs of lung cancer. They found that even when the radiologists missed a cancerous lesion, their eyes had usually paused at the site of it. Part of their brain knew there was something there; it just didn’t percolate all the way up into conscious knowledge.
In just the same way we have many thoughts that form in our head but we choose to ignore, or worse, silence them.
This is perhaps also the origin of the idea of brain-storming without criticising. The idea here is that when a team meets to come up with ideas, they sit an enlist as many ideas as possible without judging any idea. It helps to bring out some crazy ideas, which might just be better than any other idea you will get.