This method works best with traditional lick-and-stick envelopes that use water-based adhesive. Cold temperatures may make the glue brittle, allowing the flap to be lifted carefully with a fingernail or dull tool.
However, the trick is not guaranteed. Modern peel-and-stick envelopes use stronger adhesives, and tightly sealed or damp paper may still tear. Success depends on the glue, the condition of the envelope, and how carefully it is opened.
If the envelope opens, the mistake may be corrected. If not, replacing it is usually the safest solution. Either way, it serves as a reminder to slow down before sealing something important.
