Quote from note: "For the effort used to create an entire world, some people would prefer to create a single life."
A world is a terribly complex system. You are going to have different terrains, which will be split up into different nations, each one with its own government, economical system, religion, technology, etiquette, and communication (both within the nation and between nations). In order to create a fully-functional world, you will require a significant quantity of effort and energy.
A person is a terribly complex system. They have hopes, dreams, fears, thoughts (both deep and shallow), homes, other people in various roles, and the have histories, which include all of those aspects, but to a younger version of that character, all of which have worked to shape these characters into the people they currently are. In order to make a fully-fleshed out character, you will require a significant quantity of effort and energy.
As a writer, you may choose to focus on one subject or the other.
I tend to lean toward writing about worlds. I find that making these enclosed, but dynamic systems is an incredible challenge. The nature of technology to improve, leaders to degrade, and revolution to occur makes stability incredibly difficult, and if it is impossible, then I am constantly exploring how form of government ends up producing the next form of government.
I also enjoy writing about people. I find trying to capture and portray the entirety of a person's psyche an incredible challenge. There are so many factors that are simultaneously acting upon us, affecting the thoughts and decisions we make, combined with our collected history, which has shaped us greatly, that it is a wonder people can be described in any accurate way at all.
Whether you lean toward worlds or people, you will find them to be incredibly similar in their depth and complexity. If you wish to do them justice in your works, be prepared to work for it.