Theory: When dynamic types feel empty, they try to fill the void by giving themselves things to do. When static types feel empty, they try to fill the void with stuff.
What do you think? Obviously both can apply to the same person, but I think different people have different tendencies. (Some try to fill it with relationships or food/substances, but those can be classified as "things to do" or "stuff" as well, depending on how they're experiencing it.)