When a piece of bread falls to the ground, why is the buttered side always easier to touch the ground, while the buttered side is always on it?
Mathematically speaking, the probability of these two situations is equal. In fact, this is what human sensitive nerves are doing. When the buttered side of bread falls on the ground, people will relax after worrying, stop paying attention to it and soon forget it. And if the buttered side happens to be on the ground, it will make people feel very sorry and leave a deep impression on their brains.