Haridāsa offered his obeisances to the Lord and replied, “My body is all right, but my mind and intelligence are not well.”
prabhu kahe,–‘kon vyādhi, kaha ta’ nirṇaya?’
teṅho kahe,–‘saṅkhyā-kīrtana nā pūraya’
Purport by Srila Prabhupada
If one cannot complete the fixed number of rounds he is assigned, he should be considered to be in a diseased condition of spiritual life. Śrīla Haridāsa Ṭhākura is called nāmācārya. Of course, we cannot imitate Haridāsa Ṭhākura, but everyone must chant a prescribed number of rounds. In our Kṛṣṇa consciousness movement we have fixed sixteen rounds as the minimum so that the Westerners will not feel burdened. These sixteen rounds must be chanted, and chanted loudly, so that one can hear himself and others.
Sri Caitanya-caritamrta – (1975) Antya-lila 11.19-20
One may have other duties to perform under the direction of the spiritual master, but he must first abide by the spiritual master’s order to chant a certain number of rounds. In our Kṛṣṇa consciousness movement, we have recommended that the neophyte chant at least sixteen rounds. This chanting of sixteen rounds is absolutely necessary if one wants to remember Kṛṣṇa and not forget Him. Of all the regulative principles, the spiritual master’s order to chant at least sixteen rounds is most essential.
Purport by Srila Prabhupada — Sri Caitanya-caritamrta – (1975) Madhya-lila 22.113