Belief in facts or opinions from the Da’ara’ita.

I really enjoyed defining substantive and formal authority.
Either way, the rabbi does not accept the authority on facts and opinions, and on matters of taste.
I asked:
And regarding some of the facts and beliefs in the Torah, if a person concludes otherwise, how is he obligated to believe it? The cycle repeats again: if he believes otherwise, how can he deceive himself?
 
I didn’t understand the division between whether it was from the Torah or the Sanhedrin-Chazal-Talmud-accepted them in the section on opinions, beliefs, and facts.
 
I would appreciate the Rabbi’s answer.
With great respect.