Alcoholic beverages and consciousness-changing drugs darken the mind. Too much sensory stimulation and sensual indulgence also darken the mind. All activity, in fact, that absorbs one in materiality, and that lessens one's spiritual awareness, obscures the mind, reducing its clarity. Divine redemption, then, means withdrawing from identification with delusion, and becoming inwardly absorbed in the light of truth. The same is true of the mind.
Darkness enters people's consciousness because of their attachment to material grossness.
Mental clarity is affected also by clouds of doubt and restlessness, and by clouds of emotion such as fear, anger, and hatred. All these are the foes of calm feeling and intuition. Anything that prevents one from seeing life with dispassion, and therefore objectively, obscures the inner light. A Bengali friend of the author's lived in Calcutta during the unrest that attended the partition of India and Pakistan in 1948. For some days he was forced to protect himself and his family by barricading themselves in their home.