In this material world, everyone thinks that he has conquered his enemies, not understanding that his enemies are his uncontrolled mind and five senses (manaḥ ṣaṣṭhānīndriyāṇi prakṛti-sthāni karṣati (B.G.-15:7). In this material world, everyone has become a servant of the senses. Originally everyone is a servant of Kṛṣṇa, but in ignorance one forgets this, and thus one is engaged in the service of māyā through lusty desires, anger, greed, illusion, madness and jealousy. Everyone is actually dependent on the reactions of material laws, but still one thinks himself independent and thinks that he has conquered all directions. In conclusion, one who thinks that he has many enemies is an ignorant man, whereas one who is in Kṛṣṇa consciousness knows that there are no enemies but those within oneself—the uncontrolled mind and senses.
(Srimad Bhagavatam--7:8:10---purport).

One who is not connected with the Supreme (in Kṛṣṇa consciousness) can have neither transcendental intelligence nor a steady mind, without which there is no possibility of peace. And how can there be any happiness without peace?
Unless one is in Kṛṣṇa consciousness, there is no possibility of peace. So it is confirmed in the Fifth Chapter (5.29) that when one understands that Kṛṣṇa is the only enjoyer of all the good results of sacrifice and penance, that He is the proprietor of all universal manifestations, and that He is the real friend of all living entities, then only can one have real peace. Therefore, if one is not in Kṛṣṇa consciousness, there cannot be a final goal for the mind. Disturbance is due to want of an ultimate goal, and when one is certain that Kṛṣṇa is the enjoyer, proprietor and friend of everyone and everything, then one can, with a steady mind, bring about peace. Therefore, one who is engaged without a relationship with Kṛṣṇa is certainly always in distress and is without peace, however much he may make a show of peace and spiritual advancement in life. Kṛṣṇa consciousness is a self-manifested peaceful condition which can be achieved only in relationship with Kṛṣṇa.
(Bhagavad-Gita--2:66---translation and purport).

The Supreme Lord, Kṛṣṇa, is the only controller, and all living entities are controlled by Him. These living entities are His superior energy because the quality of their existence is one and the same with the Supreme, but they are never equal to the Lord in quantity of power. While exploiting the gross and subtle inferior energy (matter), the superior energy (the living entity) forgets his real spiritual mind and intelligence. This forgetfulness is due to the influence of matter upon the living entity. But when the living entity becomes free from the influence of the illusory material energy, he attains the stage called mukti, or liberation. The false ego, under the influence of material illusion, thinks, "I am matter, and material acquisitions are mine." His actual position is realized when he is liberated from all material ideas, including the conception of his becoming one in all respects with God. Therefore one may conclude that the Gītā confirms the living entity to be only one of the multi-energies of Kṛṣṇa; and when this energy is freed from material contamination, it becomes fully Kṛṣṇa conscious, or liberated.
(Bhagavad-Gita--7:5---purport).

When one's mind is in full Kṛṣṇa consciousness and one fully engages in rendering devotional service to the Lord, he becomes just like an ocean unagitated by waves. This very example is also cited in Bhagavad-gītā: one should become like the ocean. The ocean is filled by many thousands of rivers, and millions of tons of its water evaporates into clouds, yet the ocean is the same unagitated ocean. The laws of nature may work, but if one is fixed in devotional service at the lotus feet of the Lord, he is not agitated, for he is introspective. He does not look outside to material nature, but he looks in to the spiritual nature of his existence; with a sober mind, he simply engages in the service of the Lord. Thus he realizes his own self without false identification with matter and without affection for material possessions. Such a great devotee is never in trouble with others because he sees everyone from the platform of spiritual understanding; he sees himself and others in the right perspective.
(Srimad Bhagavatam---3:24:44----purport).

The symptoms of the self-realized person are given herein. The first symptom is that he is not illusioned by the false identification of the body with his true self. He knows perfectly well that he is not this body, but is the fragmental portion of the Supreme Personality of Godhead. He is therefore not joyful in achieving something, nor does he lament in losing anything which is related to his body. This steadiness of mind is called sthira-buddhi, or self-intelligence. He is therefore never bewildered by mistaking the gross body for the soul, nor does he accept the body as permanent and disregard the existence of the soul. This knowledge elevates him to the station of knowing the complete science of the Absolute Truth, namely Brahman, Paramātmā and Bhagavān. He thus knows his constitutional position perfectly well, without falsely trying to become one with the Supreme in all respects. This is called Brahman realization, or self-realization. Such steady consciousness is called Kṛṣṇa consciousness.
(Bhagavad-Gita---5:20---purport).