There are only two kinds of people in the world. For example, when a bunch of grapes is obtained, one kind of people picks the best grapes to eat first, while the other kind of people save the best grapes for last. As a rule, the first kind of people should be optimistic, because every grape he eats is the best of the remaining grapes; the second kind of people should be pessimistic, because every grape he eats is the worst of the remaining grapes. However, the reality is the opposite, because the second kind of people still have hope, while the first kind of people only have memories.