There are two kinds of people in the world: the first kind is people who belong to these two kinds, while the second kind is people who do not.
Above is just one of the classification methods. Confused?
Here is another rule of classification: there are 10 kinds of people in the world – one kind is people who know the binary system, while the other kind is people who do not.
This rule is much more difficult to understand than the first one.