The secret to success is to take refuge under the protection of the Supreme Lord. Without His sanction, nothing can be possible.
(Srimad Bhagavatam---1:10:5---purport).

The secret of success in spiritual life is in satisfying the spiritual master and thereby getting his sincere blessings.
(Srimad Bhagavatam---1:1:8---purport).

The secret of success in understanding the intricacies of knowledge of the Absolute Truth, the Personality of Godhead, is the causeless mercy of the Lord. Even in the material world, the father of many sons discloses the secret of his position to the pet sons. The father discloses the confidence unto the son whom he thinks worthy. An important man in the social order can be known by his mercy only. Similarly, one must be very dear to the Lord in order to know the Lord. The Lord is unlimited; no one can know Him completely, but one's advancement in the transcendental loving service of the Lord can make one eligible to know the Lord.
(Srimad Bhagavatam---2:9:32---purport).

One who tries to enjoy the results of his activities becomes bound by the results. One who offers the results or profits to the Supreme Personality of Godhead, however, does not become entangled in the results. This is the secret of success.
(Srimad Bhagavatam---4:30:19---purport).

Devoid of Kṛṣṇa consciousness, those who engage in material activities simply become more entangled in material bondage. They have to suffer and enjoy the actions and reactions of all activity. This Kṛṣṇa consciousness movement is therefore the greatest boon to humanity because it keeps one always engaged in Kṛṣṇa's service. The devotees think of Kṛṣṇa, act for Kṛṣṇa, eat for Kṛṣṇa, sleep for Kṛṣṇa and work for Kṛṣṇa. Thus everything is engaged in the service of Kṛṣṇa. A total life in Kṛṣṇa consciousness saves one from material contamination. As stated by Bhaktisiddhānta Sarasvatī Gosvāmī Mahārāja:
kṛṣṇa-bhajane yāhā haya anukūla
viṣaya baliyā tyāge tāhā haya bhūla
If one is so expert that he can engage everything or dovetail everything in the service of the Lord, to give up the material world would be a great blunder. One should learn how to dovetail everything in the service of the Lord, for everything is connected to Kṛṣṇa. That is the real purpose of life and secret of success.
(Srimad Bhagavatam---4:30:19---purport).

When a devotee is put into hellish conditions, he accepts them as Kṛṣṇa's mercy. He does not protest, "Oh, I am such a great devotee of Kṛṣṇa. Why have I been put into this misery?" Instead he thinks, "This is Kṛṣṇa's mercy." Such an attitude is possible for a devotee who engages in the service of Kṛṣṇa's representative. This is the secret of success.
(Srimad Bhagavatam---6:1:16---purport).

If one chants the holy name of the Lord just to make a show, not knowing the secret of success, he may increase his bile secretion, but he will never attain perfection in chanting the holy name.
(Sri Caitanya Caritamrta---1:7:95-96---purport).

This is an opportunity for everyone. If one simply follows the instructions of Śrī Caitanya Mahāprabhu, under the guidance of His representative, and chants the Hare Kṛṣṇa mantra, teaching everyone as far as possible the same principle, the contamination of the materialistic way of life will not even touch him. It does not matter whether one lives in a holy place like Vṛndāvana, Navadvīpa or Jagannātha Purī or in the midst of European cities, where the materialistic way of life is very prominent. If a devotee follows the instructions of Śrī Caitanya Mahāprabhu, he lives in the company of the Lord. Wherever he lives, he converts that place into Vṛndāvana and Navadvīpa. This means that materialism cannot touch him. This is the secret of success for one advancing in Kṛṣṇa consciousness.
(Sri Caitanya Caritamrta---2:7:129---purport).