When you trust a business friend who is actually your enemy, then he can create tha greatest danger. Ignorance is our greatest enemy.
One who is ignorant of scientific knowledge of the spirit soul does not look inside the body to find happiness in the soul; instead, he goes outside to search for happiness
Srimad bhagavatam 7.13.29,
To show them special mercy, I, dwelling in their hearts, destroy with the shining lamp of knowledge the darkness born of ignorance.
Bhagavad Gita 10.11,
Indulgence in animal killing for the taste of the tongue is the grossest kind of ignorance.
Ignorance is the cause of sinful life, and sinful life is the cause of one’s dragging on in material existence.
Bhagavad Gita 4.31,
Taking medicine without Doctor’s prescription is foolishness. Similarly reading sastra without genuine guru is ignorance.