What is the thing that your MC would never do throughout your story?
We know authors always establish rules on their lore, worldbuilding, characters, and even to themselves.
What do you think that your MC will never commit?
Like Batman's "No-Kill" rule.
This might be an unspoken rule, something that make the MC distinguish themselves from the rest of the characters, their defining moral compass and principle, or just something that will betray their character/personality once committed.
For me, since my MC is based on a historical figure, is that he will never escalate a conflict into an open confrontation (because that would betray his inspiration), and from that I can establish what will it takes for him to work himself to stay committed to his vows, of course this sometimes takes a lot of Chekov's something so things won't be so contrive, this also might slow down the story explaining the rules, laws, and operations of how these solutions will be used when it need to.