The metaphor does not mean treating every new person as dishonest or ending all trust after one bad encounter. Caution means sensible verification and correcting mistakes—not baseless accusations.
Example 1: After a loss from a vague business arrangement, someone uses clear written terms the next time, even with a trusted partner.
Example 2: If a promise has been broken, asking for verifiable assurances in a similar matter may be prudent; it does not justify condemning everyone.
مَرَّتَيْنِ is a dual form. Its ـَيْنِ ending helps express “on two occasions.”