Bhagavad Gita 8.19भूतग्रामः स एवायं भूत्वा भूत्वा प्रलीयते।रात्र्यागमेऽवशः पार्थ प्रभवत्यहरागमे ॥

Avidya (ignorance), Kama (desire) and Karma (action) are the three knots that bind the individual to Samsara. Desire is born of Avidya. Man exerts to attain and enjoy the objects of his desires. During this activity he favours some and injures others through the force of RagaDvesha (love and hatred or attraction and repulsion). Therefore he is caught in the wheel of Samsara or transmigration. He has to take birth again and again to reap the fruits of his own actions. He repeatedly comes forths and dissolves through the force of his own Karma.The individual souls have lost their independence as they are bound by ignorance, desire and activity. Therefore they are subject to the sorrows, miseries and pains of this Samsara. In order to create dispassion in their minds and a longing for liberation in their hearts, and to remove the fallacious belief that a man reaps the fruits of what he has not done or that he does not reap the fruits of what he has done, the Lord has said that all creatures involuntarily come into being again and again at the coming of the day and dissolve at the coming of the night (on account of the actions or Karmas caused by desire born of ignorance).