SB 11.20.21

Just as an expert rider intimately knows the propensities of an untamed horse and gradually brings the horse under control, an expert yogī allows the mind to reveal its materialistic propensities and then controls them through superior intelligence. A learned transcendentalist withholds and supplies sense objects so that the mind and senses remain fully controlled, just as the horseman sometimes pulls sharply on the reins and sometimes allows the horse to run freely. The rider never forgets his actual goal or destination, and eventually places the horse on the right path. Similarly, a learned transcendentalist, even though sometimes allowing the senses to act, never forgets the goal of self-realization, nor does he allow the senses to engage in sinful activity. Excessive austerity or restriction may result in great mental disturbance, just as pulling excessively on the reins of a horse may cause the horse to rear up against the rider. The path of self-realization depends upon clear intelligence, and the easiest way to acquire such expertise is surrender to Lord Kṛṣṇa. The Lord says in Bhagavad-gītā (10.10) :

teṣāṁ satata-yuktānāṁ bhajatāṁ prīti-pūrvakam dadāmi buddhi-yogaṁ taṁ yena mām upayānti te

One may not be a great scholar or spiritual intellect, but if one is sincerely engaged in loving service to the Lord without personal envy or personal motivation the Lord will reveal from within the heart the methodology required to control the mind. Expertly riding the waves of mental desire, a Kṛṣṇa conscious person does not fall from the saddle, and he eventually rides all the way back home, back to Godhead.