Even if an unlettered person purposely commits a sin or neglects to perform a mitzvah, his sin is considered unintentional and minor, for it lacks the basic element of complete willfulness: rebellion, denial of a supreme Master, a conscious turning away from God's will.
This person does not truly understand the meaning of holiness and views God and His mitzvot as unclear concepts.
He is thus considered to be acting unwittingly, like a child who breaks an expensive item whose value he cannot appreciate.
Even when such a person acts knowingly, his knowledge does not extend to a full understanding.
To be willful, a person must be aware.
When his consciousness is on a low level, when he does not adequately understand the meaning of sin and mitzvot, he cannot be judged on the same scale as someone who does know and comprehend.
–Rabbi Adin Steinsaltz
From Understanding the Tanya, Ch.30 by Rabbi Adin Steinsaltz