Knowledge is what all people require for success in life.
Since small age, kids are tought at school so they can be someone in life. Without knowledge is like living without a purpose. As we know, smart people are always searched and they always get high paied jobs.
But, why as important as air? Because there is nothing more precious and expensive than knowledge. For example, if you're smart, you will have a lot of friends because you will be interesting. Now really, who likes boring and stupid people? Yes that's why we need knowledge !
