According to Tabatabaei, there is a quality of man that protects him from committing sin or error. Tabatabaei equates this quality with knowledge. Virtues such as bravery, chastity, and generosity are forms of knowledge, deeply rooted in the human psyche, that enable a person to abstain from indulging in extremes of behavior: for example, cowardice and recklessness, austerity and dissipation, or miserliness and extravagance. An increase in knowledge means increased obedience to God. In ordinary people with imperfect knowledge, virtue can be overpowered and tainted by desires and vices. Prophets are bestowed with supreme knowledge and thus a that always remain unaffected by whims and vices. This supreme knowledge in Prophets is Ismah. Ismah does not nullify the Prophets' free will to choose whether to commit sin or not.