SB 5.11.6

duḥkhaṁ sukhaṁ vyatiriktaṁ ca tīvraṁ
 kālopapannaṁ phalam āvyanakti
āliṅgya māyā-racitāntarātmā
 sva-dehinaṁ saṁsṛti-cakra-kūṭaḥ
Synonyms: 
duḥkham — unhappiness due to impious activities; sukham — happiness due to pious activities; vyatiriktam — illusion; ca — also; tīvram — very severe; kāla-upapannam — obtained in the course of time; phalam — the resultant action; āvyanakti — creates; āliṅgya — embracing; māyā-racita — created by material nature; antaḥ-ātmā — the mind; sva-dehinam — the living being himself; saṁsṛti — of the actions and reactions of material existence; cakra-kūṭaḥ — which deceives the living entity into the wheel.
Translation: 
The materialistic mind covering the living entity’s soul carries it to different species of life. This is called continued material existence. Due to the mind, the living entity suffers or enjoys material distress and happiness. Being thus illusioned, the mind further creates pious and impious activities and their karma, and thus the soul becomes conditioned.
Purport: 

Mental activities under the influence of material nature cause happiness and distress within the material world. Being covered by illusion, the living entity eternally continues conditioned life under different designations. Such living entities are known as nitya-baddha, eternally conditioned. On the whole, the mind is the cause of conditioned life; therefore the entire yogic process is meant to control the mind and the senses. If the mind is controlled, the senses are automatically controlled, and therefore the soul is saved from the reactions of pious and impious activity. If the mind is engaged at the lotus feet of Lord Kṛṣṇa (sa vai manaḥ kṛṣṇa-padāravindayoḥ), the senses are automatically engaged in the Lord’s service. When the mind and senses are engaged in devotional service, the living entity naturally becomes Kṛṣṇa conscious. As soon as one always thinks of Kṛṣṇa, he becomes a perfect yogī, as confirmed in Bhagavad-gītā (yoginām api sarveṣāṁ mad-gatenāntarātmanā). This antarātmā, the mind, is conditioned by material nature. As stated here, māyā-racitāntarātmā sva-dehinaṁ saṁsṛti-cakra-kūṭaḥ: the mind, being most powerful, covers the living entity and puts him in the waves of material existence.