Things we can't have

We all want something but we know we will never get it. That want will always stay as a want because there is one string attached to it; you can't have it. Why do we want things that we can't have or that isn't obtainable? We all know that we can't have it but we still want it. We get over it but deep down we still wish that we could have it. Why? What would life be if you got everything you wanted? What would you want if you have everything in life? Why would you want it if you have so much already?