Exceptions, concessions and purpose

除非你亲自解释，他才会相信 states personal explanation as necessary. It does not guarantee belief in every real-world circumstance; it expresses the speaker's condition for the claim.

Pitfall: The condition is a required exception, not merely one helpful possibility.

除非下雨，否则照常出发: no rain implies planned departure. If rain occurs, the sentence releases that default; the exact alternative may remain unstated. Do not automatically infer a fully specified cancellation procedure.

Pitfall: The second clause applies when the 除非 condition is false.

Pitfall: The clause can be hypothetical; do not automatically treat the failure as fact.

Pitfall: The purpose clause states an intended use, not necessarily an achieved consequence.