What is the difference between light and darkness? You will understand the difference the moment you put your hands to cover your eyes. The moment you put your hands on your eyes, it will become dark and the moment you take off your hands, you will see light.
Doubts are the hands and mind is the eye. Take doubts off your mind and you will see that you will be able to perceive everything clearly. Doubts create negativity which stop you from thinking clearly and create darkness in your mind.