Multiple commentators, especially A.T. Robertson, stress that the Greek grammar is key. The phrases 'doeth no sin' and 'cannot sin' use a tense that indicates a continuous, habitual practice. The verse is not teaching that Christians achieve sinless perfection. Rather, it means a person truly born of God cannot make sin the ongoing, characteristic pattern of their life. As Charles Spurgeon illustrates, a sheep may fall into the mire, but it does not wallow in it like a pig.