This expression is about human nature: The expression is comparing the human brain to a machine (think of a computer - there is a standard way that all computers are "wired" and "put together" to work the same way when you press the "on" button). This analogy between brain and machine is used to express something essential about human nature that we can't change. The expression is used to describe how all people are "wired" (or "hardwired") from birth to behave or think a certain way. So, the writer of the essay believes that humans are born with specific traits/characteristics that prevents them from being happy. I hope this helps! :-)