If it's that hard to fall asleep, then you don't need a nap. Problem solved. Depending on their job, diet, exercise, age, etc., some people just really really really really need a 10-15 minute nap in the early afternoon to get through the rest of the day. The need comes over you quickly, and you either do it or spend the rest of the day struggling to stay awake and focused on your work. I don't think anyone is suggesting that people who aren't actually tired take naps.