Sincerity Does Not Guarantee Authenticity
Sincerity is usually treated as evidence of truthfulness. If I genuinely believe what I am saying, I am sincere. That matters. It does not settle the question of authenticity.
A person can sincerely defend an explanation that protects them from seeing their own contribution. They can sincerely believe they had no choice while ignoring choices they did not want to make. They can sincerely describe themselves as generous, fair, or open while leaving contradictory behavior outside the story.
Sincerity concerns whether the account is genuinely held. Authenticity asks whether we are willing to include what the account leaves out. This distinction should not become another tool for accusing people of hidden motives. Its strongest use is first-person.
What am I certain about? What does that certainty allow me not to examine? I may be completely sincere. The inquiry can still continue.