Even though we've all experienced most temperatures, we have selective memory about what they're actually like, especially when they're more balmy than brutal. Ask us in the winter if 65 degrees is appropriate shorts weather and we'll stare blankly. Ask us in the summer if five below requires taking a cab to work, and we won't be able to give you a confident answer. And, if we're traveling to a location where the temperature is a good 20 degrees off from what we're used to, that's reason enough to purposefully overpack — because, is 72 and sunny beach weather, or not?