The main helper in bhajana-sādhana is the mind, the Lord of the senses.
The mind of a materialistic person is by nature restless and attached to the sense-objects.

In the Bhagavad Gītā (6.34) Arjuna tells the Lord:

cañcalaṁ hi manaḥ kṛṣṇa pramāthi balavad dṛḍham
tasyāhaṁ nigrahaṁ manye vāyor iva suduṣkaram

“O Kṛṣṇa! The mind is restless, disturbing the senses, powerful and tenacious. To control him seems to be as difficult as to control the wind (in our bodies, by means of kumbhaka and recaka- exercises).”

The Lord agreed with this and said:

asaṁśayaṁ mahā-bāho mano durnigrahaṁ calam
abhyāsena tu kaunteya vairāgyeṇa ca gṛhyate
(Bhagavad Gītā 6,35)

“O mighty-armed one! Undoubtledly it is very difficult to subdue the naturally restless mind, but it can be accomplished through exercise and detachment.” 

By understanding how powerful and how hard to subdue the mind is, the sādhaka will slowly tread on the path of auspiciousness.

Any stream of thoughts which emanates from our minds keeps a saṁskāra (impression, mental conditioning) within our (sub-) consciousness, and the aggregate of these saṁskāras form our svabhāva (nature).

Just as our present nature is the result of previous saṁskāras, our future nature will be the result of our present thoughts and actions. By giving up our mundane saṁskāras and developing a spiritual saṁskāra, we can gradually control the mind and tread on the path of bhajana. There is no other way.

Śrī Raghunātha very tenderly addresses his mind by saying: “O mind, my brother! I hold your feet and I pray to you with flattering words, please listen! First of all, always give up dambha, or pride.

False ego, deceitfulness, and crookedness, these are all considered to be dambha. For innumerable births our saṁskāra has been the identification with our material bodies and everything related to it. This consciousness is a great obstacle in devotional practice.

abhimānī bhakti-hīna, jaga mājhe
sei dīna, vṛthā tāra aśeṣa bhāvanā
(Prema Bhakti Candrikā)

“The proud non-devotees are the lowest people in the world. Their endless thoughts are all in vain!”

To destroy false pride devotees practice humility; hence humility is called the life-force of devotional practice.
Deceitfulness and duplicity (thinking in one way and acting in another) are other great obstacles in devotional practice.

The Lord will never want to bestow His mercy on a crooked person, therefore Śrīpāda says:

“O mind! Always give up dambha, or vanity, which is a powerful obstacle to bhajana, and instead become very attached to some other objects!”
(Śrī Rādhākuṇḍa Mahānta Paṇḍita Śrī Ananta Dās Bābājī Mahārāja)