In many large cities of the world, thieves hunt travelers from the shadows. They watch you take pictures at monuments, eat tapas at an outdoor cafe, and if you are unlucky, they will follow your steps with excited eyes as you fall into one of their traps. A few weeks ago while visiting Quito, thieves dumped a bucket of crap on me from a rooftop and then jumped me for my camera. It was horrible.

Fear-mongering aside, travelers are chosen as targets because they are not completely in tune to their surroundings. Maybe you are jet lagged, or you just ate a dangerous meal that has left you weak with intestinal anxiety, or you are lost in …