Devotee: Why is it sometimes if we are sincerely trying to serve Kṛṣṇa we still make mistakes? We make in our service some mistakes.
Prabhupāda: You must always remember that service means by the order of the master. So if you should always be ready to take order from the master, there will be no mistake.
Devotee: Does that mean that our mistakes come from the false ego?
Prabhupāda: Yes. When you disobey the order of master, that is mistake.