Kṛṣṇa has given independence to all jīvas – to some degree, not fully – and with that independence the jīva may or may not do what Kṛṣṇa wants him to do. If a man wants to serve Kṛṣṇa, he is required to strictly follow the instructions in this verse, thinking, “I should not be angry. I must follow tṛṇād api sunīcena. This will bring bhakti.” A person who wishes to advance in bhakti is never allowed to quarrel with anyone for his own gain.
Bharata and Śrī Rāmacandra quarrelled with each other, but for what reason? Bharata told Śrī Rāma, “I will not take the kingdom. You must take it.” Rāma replied, “No, you should take it.” They were quarrelling only for the purpose of giving, not for taking. On the other hand, Duryodhana and the Pāṇḍavas were fighting for taking.
“I must attain love for Rādhā and Kṛṣṇa. By following the principles of tṛṇād api sunīcena (thinking oneself more insignificant and lowly than the straw in the street, etc.), I can attain Their service.” When one develops this mood, he will strongly follow these principles.
Read and follow Upadeśāmṛta. Amṛta means ‘nectar.’ Why are these instructions (upadeśa) called nectar? It is because following them gives kṛṣṇa-bhakti up to rādhā-dāsyam (personal service to Śrīmatī Rādhikā). Rādhā-dāsyam is the aim and object of our life and sādhana-bhajana. If one truly desires this attainment, he will follow Upadeśāmṛta. If we have everything in our life except bhakti, we really have nothing; whereas if we have only bhakti, our life is successful.
There are two additional principles to follow: strictly reject what is not favourable for kṛṣṇa-bhakti and strongly accept what is favourable. By such practice, anarthas will gradually diminish and you will become a pure bhakta.

—Śrīla Bhaktivedānta Nārāyaṇa Mahārāja