Why do they call it common sense, when it's so rare?

Why is vanilla ice cream white, when vanilla extract is brown?

What would a chair look like, if your knees bent the other way?

Why do our noses run and our feet smell?

Why is, it that when you transport something by car, it's called a shipment, but when you transport something by ship, it's called cargo?

If Barbie is so popular, why do you have to buy her friends?